听力原文：There are exceptions to the rule of male insects being smaller than the females,

and some of these exceptions are intelligible. Size and strength would be advantage to the males which fight for the possession of the females, and in these cases, as with the stag-beetle, the males are larger than the females. There are, however, other beetles which are not known to fight together, of which the males exceed the females in size. But in some of the other cases, as with the huge Dynastes and Megasoma, we can see that there would be no necessity for the males to be smaller in order to be matured before them, for these beetles are not short-lived.

Which of the following is true？

A．Male insects are always smaller than females.

B．In a given species nature provides differences between sexes to secure successful production.

C．Size and strength protect females from other females.

D．Longevity is characteristic of the Dynastes and Megasoma.