我国档案工作基本原则的三个部分中，（）是核心。

A、统一领导，分级管理

B、维护档案的完整与安全

C、便于社会各方面利用

D、便于保管

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.