Cho dãy số $\left(u_n\right)$ với $\left\{\begin{array}{l}{u}_1=1\\ u_{n+1}=u_n+(-1{)}^{2n+1}\end{array}\right.$

Số hạng tổng quát $u_n$của dãy số là biểu thức 

Question 27: What is the main idea presented in paragraph 3? 

Of all modern instruments, the violin is apparently one of the simplest. It consist in essence of a hollow, varnished wooden sound box, or resonator, and a long neck covered with a fingerboard, along which four strings are stretched at high tension. The beauty of design, shape, and decoration is no accident, the proportions of the instrument are determined entirely by acoustical considerations. Its simplicity of appearance is deceptive. About 70 parts are involved in the construction of a violin. Its tone and its outstanding range of expressiveness make it an ideal solo instrument. No less important, however, is its role as an orchestral and chamber instrument. In combination with the larger and deeper-sounding members of the same family, the violins form the nucleus of the modem symphony orchestra. The violin has been in existence since about 1550. Its importance as an instrument in its own right dates from the early 1600’s, when it first became standard in Italian opera orchestras. Its stature as an orchestral instrument was raised further when in 1626 Louis XIII of France established at his court the orchestra known as Les vinq-quatre violons du Roy (The King's 24 Violins), which was to become widely famous later in the century. In its early history, the violin had a dull and rather quiet tone resulting from the fact that the strings were thick and were attached to the body of the instrument very loosely. During the eighteenth and nineteenth century exciting technical changes were inspired by such composer-violinists as Vivaldi and Tartini. Their instrumental compositions demanded a fuller, clearer, and more brilliant tone that was produced by using thinner strings and a far higher string tension. Small changes had to be made to the violin's internal structure and to the fingerboard so that they could withstand the extra strain. Accordingly, a higher standard of performance was achieved, in terms of both facility and interpretation. Left-hand technique was considerably elaborated, and new fingering patterns on the fingerboard were developed for very high notes.

Read the following passage and mark the letters A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.

Scientists do not yet thoroughly understand just how the body of an individual becomes sensitive to a substance that is harmless or even wholesome for the average person. Milk, wheat, and egg, for example, rank among the most healthful and widely used foods. Yet these foods can cause persons sensitive to them to suffer greatly. At first, the body of the individual is not harmed by coming into contact with the substance. After a varying interval of time, usually longer than a few weeks, the body becomes sensitive to it, and an allergy has begun to develop. Sometimes it's hard to figure out if you have a food allergy, since it can show up so many different ways. Your symptoms could be caused by many other problems. You may have rashes, hives, joint pains, mimicking arthritis, headaches, irritability, or depression. The most common food allergies are to milk, eggs, seafood, wheat, nuts, seeds, chocolate, oranges, and tomatoes. Many of these allergies will not develop if these foods are not fed to an infant until her or his intestines mature at around seven months. Breast milk also tends to be protective. Migraines can be set off by foods containing tyramine, phenathylamine, monosodium glutamate, or sodium nitrate. Common foods which contain these are chocolate, aged cheeses, sour cream, red wine, pickled herring, chicken livers, avocados, ripe bananas, cured meats, many Oriental and prepared foods (read the labels!). Some people have been successful in treating their migraines with supplements of B-vitamins, particularly B6 and niacin. Children who are hyperactive may benefit from eliminating food additives, especially colorings, and foods high in salicylates from their diets. A few of these are almonds, green peppers, peaches, tea, grapes. This is the diet made popular by Benjamin Feingold, who has written the book “Why your Child is Hyperactive”. Other researchers have had mixed results when testing whether the diet is effective. 

Question The topic of this passage is _____________.         

Read the following passage and mark the letters A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.

Scientists do not yet thoroughly understand just how the body of an individual becomes sensitive to a substance that is harmless or even wholesome for the average person. Milk, wheat, and egg, for example, rank among the most healthful and widely used foods. Yet these foods can cause persons sensitive to them to suffer greatly. At first, the body of the individual is not harmed by coming into contact with the substance. After a varying interval of time, usually longer than a few weeks, the body becomes sensitive to it, and an allergy has begun to develop. Sometimes it's hard to figure out if you have a food allergy, since it can show up so many different ways. Your symptoms could be caused by many other problems. You may have rashes, hives, joint pains, mimicking arthritis, headaches, irritability, or depression. The most common food allergies are to milk, eggs, seafood, wheat, nuts, seeds, chocolate, oranges, and tomatoes. Many of these allergies will not develop if these foods are not fed to an infant until her or his intestines mature at around seven months. Breast milk also tends to be protective. Migraines can be set off by foods containing tyramine, phenathylamine, monosodium glutamate, or sodium nitrate. Common foods which contain these are chocolate, aged cheeses, sour cream, red wine, pickled herring, chicken livers, avocados, ripe bananas, cured meats, many Oriental and prepared foods (read the labels!). Some people have been successful in treating their migraines with supplements of B-vitamins, particularly B6 and niacin. Children who are hyperactive may benefit from eliminating food additives, especially colorings, and foods high in salicylates from their diets. A few of these are almonds, green peppers, peaches, tea, grapes. This is the diet made popular by Benjamin Feingold, who has written the book “Why your Child is Hyperactive”. Other researchers have had mixed results when testing whether the diet is effective. 

Question According to the passage, the difficulty in diagnosing allergies to foods is due to ___________.         

Read the following passage and mark the letters A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.

Scientists do not yet thoroughly understand just how the body of an individual becomes sensitive to a substance that is harmless or even wholesome for the average person. Milk, wheat, and egg, for example, rank among the most healthful and widely used foods. Yet these foods can cause persons sensitive to them to suffer greatly. At first, the body of the individual is not harmed by coming into contact with the substance. After a varying interval of time, usually longer than a few weeks, the body becomes sensitive to it, and an allergy has begun to develop. Sometimes it's hard to figure out if you have a food allergy, since it can show up so many different ways. Your symptoms could be caused by many other problems. You may have rashes, hives, joint pains, mimicking arthritis, headaches, irritability, or depression. The most common food allergies are to milk, eggs, seafood, wheat, nuts, seeds, chocolate, oranges, and tomatoes. Many of these allergies will not develop if these foods are not fed to an infant until her or his intestines mature at around seven months. Breast milk also tends to be protective. Migraines can be set off by foods containing tyramine, phenathylamine, monosodium glutamate, or sodium nitrate. Common foods which contain these are chocolate, aged cheeses, sour cream, red wine, pickled herring, chicken livers, avocados, ripe bananas, cured meats, many Oriental and prepared foods (read the labels!). Some people have been successful in treating their migraines with supplements of B-vitamins, particularly B6 and niacin. Children who are hyperactive may benefit from eliminating food additives, especially colorings, and foods high in salicylates from their diets. A few of these are almonds, green peppers, peaches, tea, grapes. This is the diet made popular by Benjamin Feingold, who has written the book “Why your Child is Hyperactive”. Other researchers have had mixed results when testing whether the diet is effective.

Question The word "symptoms" is closest in meaning to ___________.         

Read the following passage and mark the letters A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.

Scientists do not yet thoroughly understand just how the body of an individual becomes sensitive to a substance that is harmless or even wholesome for the average person. Milk, wheat, and egg, for example, rank among the most healthful and widely used foods. Yet these foods can cause persons sensitive to them to suffer greatly. At first, the body of the individual is not harmed by coming into contact with the substance. After a varying interval of time, usually longer than a few weeks, the body becomes sensitive to it, and an allergy has begun to develop. Sometimes it's hard to figure out if you have a food allergy, since it can show up so many different ways. Your symptoms could be caused by many other problems. You may have rashes, hives, joint pains, mimicking arthritis, headaches, irritability, or depression. The most common food allergies are to milk, eggs, seafood, wheat, nuts, seeds, chocolate, oranges, and tomatoes. Many of these allergies will not develop if these foods are not fed to an infant until her or his intestines mature at around seven months. Breast milk also tends to be protective. Migraines can be set off by foods containing tyramine, phenathylamine, monosodium glutamate, or sodium nitrate. Common foods which contain these are chocolate, aged cheeses, sour cream, red wine, pickled herring, chicken livers, avocados, ripe bananas, cured meats, many Oriental and prepared foods (read the labels!). Some people have been successful in treating their migraines with supplements of B-vitamins, particularly B6 and niacin. Children who are hyperactive may benefit from eliminating food additives, especially colorings, and foods high in salicylates from their diets. A few of these are almonds, green peppers, peaches, tea, grapes. This is the diet made popular by Benjamin Feingold, who has written the book “Why your Child is Hyperactive”. Other researchers have had mixed results when testing whether the diet is effective. 

Question What can be inferred about babies from this passage?             

Read the following passage and mark the letters A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.

Scientists do not yet thoroughly understand just how the body of an individual becomes sensitive to a substance that is harmless or even wholesome for the average person. Milk, wheat, and egg, for example, rank among the most healthful and widely used foods. Yet these foods can cause persons sensitive to them to suffer greatly. At first, the body of the individual is not harmed by coming into contact with the substance. After a varying interval of time, usually longer than a few weeks, the body becomes sensitive to it, and an allergy has begun to develop. Sometimes it's hard to figure out if you have a food allergy, since it can show up so many different ways. Your symptoms could be caused by many other problems. You may have rashes, hives, joint pains, mimicking arthritis, headaches, irritability, or depression. The most common food allergies are to milk, eggs, seafood, wheat, nuts, seeds, chocolate, oranges, and tomatoes. Many of these allergies will not develop if these foods are not fed to an infant until her or his intestines mature at around seven months. Breast milk also tends to be protective. Migraines can be set off by foods containing tyramine, phenathylamine, monosodium glutamate, or sodium nitrate. Common foods which contain these are chocolate, aged cheeses, sour cream, red wine, pickled herring, chicken livers, avocados, ripe bananas, cured meats, many Oriental and prepared foods (read the labels!). Some people have been successful in treating their migraines with supplements of B-vitamins, particularly B6 and niacin. Children who are hyperactive may benefit from eliminating food additives, especially colorings, and foods high in salicylates from their diets. A few of these are almonds, green peppers, peaches, tea, grapes. This is the diet made popular by Benjamin Feingold, who has written the book “Why your Child is Hyperactive”. Other researchers have had mixed results when testing whether the diet is effective.

Question  The author states that the reason that infants need to avoid certain foods related to allergies has to do with the infant's ___________.         

Read the following passage and mark the letters A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.

Scientists do not yet thoroughly understand just how the body of an individual becomes sensitive to a substance that is harmless or even wholesome for the average person. Milk, wheat, and egg, for example, rank among the most healthful and widely used foods. Yet these foods can cause persons sensitive to them to suffer greatly. At first, the body of the individual is not harmed by coming into contact with the substance. After a varying interval of time, usually longer than a few weeks, the body becomes sensitive to it, and an allergy has begun to develop. Sometimes it's hard to figure out if you have a food allergy, since it can show up so many different ways. Your symptoms could be caused by many other problems. You may have rashes, hives, joint pains, mimicking arthritis, headaches, irritability, or depression. The most common food allergies are to milk, eggs, seafood, wheat, nuts, seeds, chocolate, oranges, and tomatoes. Many of these allergies will not develop if these foods are not fed to an infant until her or his intestines mature at around seven months. Breast milk also tends to be protective. Migraines can be set off by foods containing tyramine, phenathylamine, monosodium glutamate, or sodium nitrate. Common foods which contain these are chocolate, aged cheeses, sour cream, red wine, pickled herring, chicken livers, avocados, ripe bananas, cured meats, many Oriental and prepared foods (read the labels!). Some people have been successful in treating their migraines with supplements of B-vitamins, particularly B6 and niacin. Children who are hyperactive may benefit from eliminating food additives, especially colorings, and foods high in salicylates from their diets. A few of these are almonds, green peppers, peaches, tea, grapes. This is the diet made popular by Benjamin Feingold, who has written the book “Why your Child is Hyperactive”. Other researchers have had mixed results when testing whether the diet is effective. 

Question The word "these" refers to ___________. 

Read the following passage and mark the letters A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.

Scientists do not yet thoroughly understand just how the body of an individual becomes sensitive to a substance that is harmless or even wholesome for the average person. Milk, wheat, and egg, for example, rank among the most healthful and widely used foods. Yet these foods can cause persons sensitive to them to suffer greatly. At first, the body of the individual is not harmed by coming into contact with the substance. After a varying interval of time, usually longer than a few weeks, the body becomes sensitive to it, and an allergy has begun to develop. Sometimes it's hard to figure out if you have a food allergy, since it can show up so many different ways. Your symptoms could be caused by many other problems. You may have rashes, hives, joint pains, mimicking arthritis, headaches, irritability, or depression. The most common food allergies are to milk, eggs, seafood, wheat, nuts, seeds, chocolate, oranges, and tomatoes. Many of these allergies will not develop if these foods are not fed to an infant until her or his intestines mature at around seven months. Breast milk also tends to be protective. Migraines can be set off by foods containing tyramine, phenathylamine, monosodium glutamate, or sodium nitrate. Common foods which contain these are chocolate, aged cheeses, sour cream, red wine, pickled herring, chicken livers, avocados, ripe bananas, cured meats, many Oriental and prepared foods (read the labels!). Some people have been successful in treating their migraines with supplements of B-vitamins, particularly B6 and niacin. Children who are hyperactive may benefit from eliminating food additives, especially colorings, and foods high in salicylates from their diets. A few of these are almonds, green peppers, peaches, tea, grapes. This is the diet made popular by Benjamin Feingold, who has written the book “Why your Child is Hyperactive”. Other researchers have had mixed results when testing whether the diet is effective. 

Question Which of the following was a suggested treatment for migraines in the passage?         

Read the following passage and mark the letters A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.

Scientists do not yet thoroughly understand just how the body of an individual becomes sensitive to a substance that is harmless or even wholesome for the average person. Milk, wheat, and egg, for example, rank among the most healthful and widely used foods. Yet these foods can cause persons sensitive to them to suffer greatly. At first, the body of the individual is not harmed by coming into contact with the substance. After a varying interval of time, usually longer than a few weeks, the body becomes sensitive to it, and an allergy has begun to develop. Sometimes it's hard to figure out if you have a food allergy, since it can show up so many different ways. Your symptoms could be caused by many other problems. You may have rashes, hives, joint pains, mimicking arthritis, headaches, irritability, or depression. The most common food allergies are to milk, eggs, seafood, wheat, nuts, seeds, chocolate, oranges, and tomatoes. Many of these allergies will not develop if these foods are not fed to an infant until her or his intestines mature at around seven months. Breast milk also tends to be protective. Migraines can be set off by foods containing tyramine, phenathylamine, monosodium glutamate, or sodium nitrate. Common foods which contain these are chocolate, aged cheeses, sour cream, red wine, pickled herring, chicken livers, avocados, ripe bananas, cured meats, many Oriental and prepared foods (read the labels!). Some people have been successful in treating their migraines with supplements of B-vitamins, particularly B6 and niacin. Children who are hyperactive may benefit from eliminating food additives, especially colorings, and foods high in salicylates from their diets. A few of these are almonds, green peppers, peaches, tea, grapes. This is the diet made popular by Benjamin Feingold, who has written the book “Why your Child is Hyperactive”. Other researchers have had mixed results when testing whether the diet is effective.  

Question According to the article, the Feingold diet is NOT ___________.         

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions:

Baseball evolved from a number of different ball-and stick games (paddle ball, trap ball, one-old-cat, rounders, and town ball) originating in England. As early as the American Revolution, it was noted that troops played “baseball” in their free time. In 1845 Alexander Cartwright formalized the New York Knickerbockers version of the game: a diamond shaped infield, with bases ninety feet apart, three strikers – you’re – out, batter out on a caught ball, three outs per inning, a nine man team. “The New York Game” spread rapidly, replacing earlier localized forms. From its beginnings, baseball was seen as a way of satisfying the recreational needs of an increasingly urban – industrial society. At its inception it was it was played by and for gentlemen. A club might consist of 40 members. The president would appoint two captains who would choose teams from among the members. Games were played on Monday and Thursday afternoons, with the losers often providing a lavish evening’s entertainments for the winners. During the 1850 - 70 period the game was changing, however, with increasing commercialism (charging admission), under – the – table payments to exceptional to players, and gambling on the outcome of games. By 1868 it was said that a club would have their regular professional ten, an amateur first - nine, and their "muffins" (the gently duffers who once ran the game). Beginning with the first openly all – salaried team (Cincinnati’s Red Stocking Club) in 1869, the 1870 - 1890 period saw the complete professionalization of baseball, including formation of the National Association of Professional baseball players in 1871. The National League of Professional Baseball Clubs was formed in 1876, run by business-minded invertors in joint-stock company clubs. The 1880s has been called Major League Baseball’s “Golden Age”. Profits soared, player’s salaries rose somewhat, a season of 84 games became one of 132, a weekly periodical “The sporting News” came into being, wooden stadiums with double-deck stands replaced open fields, and the standard refreshment became hot dogs, soda pop and peanuts. In 1900 the Western League based in the growing cities of the Mid-west proclaimed itself the American League.

Question 18: Which of the following is NOT mentioned as a feature of the 1880s “Golden Age”?