Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35:
The current global extinction rate is estimated at about 20,000 species per year, exponentially greater than the background extinction rate. Many (31) _____ believe that we are in the middle of the greatest mass extinction episode since the disappearance of the dinosaurs 65 million years ago. From what is known about present-day populations and from (32) _____ theory, the change in either the physical or the biological environment is the key to extinction. However, the vulnerability of a species depends (33) _____ a wide variety of factors, such as its total population size, geographical distribution, reproductive ability, ecological relations with other species, and genetic characteristics. For example, more emphasis is put on the greater vulnerability of species that reproduce slowly as contrasted with those that reproduce (34) _____. Other factors, such as food-plant specialization, may make many fast reproducers more vulnerable than species that reproduce more slowly. No matter (35) _____ fast an insect species that depends on a certain plan can reproduce; it will still go extinct if that plant's habitat is destroyed. It has been estimated that about one half billion species have lived at one time or another, and today's existing species are only 2% of those that have ever evolved. The other 98% have either died out or evolved into something sufficiently different to be called a new species.
Question 31:
