题目内容：

    Bats are the only mammals (哺乳动物) that can fly a great distance, but they have another ability. Many bats live a very long time for an animal of their size. European researchers are studying bats to understand why they live so long. They hope to make discoveries aimed at fighting the aging process in human beings.

Last week, the group of scientists said they had identified important biological qualities in some bat species. The group studied bat’s chromosomes (染色体), a line of genes found in the nucleus of cells. The scientists were most interested in structures connected to the ends of chromosomes. They are called telomeres (端粒), which protect the ends of chromosomes and shorten each time a cell divides (分裂). Scientists believed this shortening process causes cells to break down. They said this is what causes aging.

The European researchers studied 493 bats from four bat species. The group used information that had been gathered over more than 60 years. Of these animals, the greater mouse-eared bats generally lived the longest, an average of 37 years. The scientists said this and a related species, which are grouped together under the name Myotis, have telomeres that do not shorten with age. One Myotis bat holds the record for the oldest age, reaching 41 years. The scientists' findings suggested that these bats' cells have the ability to maintain and repair their telomeres. This, they said, helps guard bats against the aging process.

Based on its body size, a bat like the greater mouse-eared bat would  expected to live four years. But, these mammals have been found to live nearly 10 times longer than that. The scientists found that only 19 species of mammals live longer than humans when their body size is considered. Eighteen of these are bats.

1.What's the main purpose of European researchers studying bats?

A.To learn the living habits of bats.

B.To find out why bats enjoy a long life.

C.To try to understand why bats can fly as mammals.

D.To discover a good way to prevent human beings from aging.

2.What does the second paragraph mainly explain to us?

A.The structures of bats' chromosomes.

B.What causes aging biologically.

C.The functions of telomeres

D.What causes cells to break down.

3.Why do the greater mouse-eared bats live so long?

A.Because they are grouped together under the name Myotis.

B.Because their telomeres decrease with age.

C.Because their cells are able to keep and fix their telomeres

D.Because their bodies produce more telomeres than human beings

4.What can we know from the last paragraph?

A.Bats live 10 times longer than human beings.

B.Bats enjoy the longest life among mammals

C.Bats like the greater mouse-eared bats should have lived longer.

D.Most of the mammals living longer than human beings considering their body size are bats.