She walked home by herself at night, _____ she knew that it was dangerous.

A．once

B．as

C．unless

D．although

下丘脑和垂体在人体内分泌活动中起重要的调节作用：

图中垂体后叶释放的抗利尿激素的主要作用是（），从而降低了血浆渗透压。