My sister isn’t in. ________ she comes back, I’ll let her call you back.

A．While

B．Until

C．Before

D．When

瓶组式细水雾系统备用状态下，储水容器处于（）状态，储气容器处于（）状态。

A.常压，高压

B.常压，低压

C.低压，常压

D.高压，常压