.

— When did they come back last night?

— It was midnight ____ all of us were sleeping.

A．that

B．when

C．which

D．in which

需要两个杂交过程检测一个产物的PCR产物检测方法（）。

A.PCR-ELISA法

B.凝胶电泳分析法

C.微孔板夹心杂交法

D.点杂交分析

E.放射自显影法