They were all so tired that they could ______.

A．do nothing but sleep

B．do anything but sleep

C．do nothing but to sleep

D．do anything but to sleep

马斯洛需求层次理论中位于最底层的需求是（）。

A.自我实现

B.生理的需求

C.安全的需求

D.友爱和归属的需求