Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the best option for each of the blanks.
Any change in one part of an ecosystem can cause changes in other parts. Droughts, storms and fires can change ecosystems. Some changes harm ecosystems. If there is too ___26__ rainfall, plants will not have enough water to live. If a kind of plant dies off, the animals that feed on it may also die or move away. Some changes are good for ecosystems. Some pine forests need fire for the pine trees to reproduce. The seeds are sealed inside pinecones. Heat from a forest fire melts the seal and lets the seeds ___27___. Polluting the air, soil, and water can harm ecosystems. Building ___28___ on rivers for electric power and irrigation can harm ecosystems around the rivers. Bulldozing wetlands and cutting down ___29___ destroy ecosystems. Ecologists are working with companies and governments to find better ways of catching fish, cutting down trees, and building dams. They are looking for ways to get food, lumber, and other products for people ___30___ causing harm to ecosystems.
Question 27:
