I wonder __________ that made him so upset yesterday.

A．it was what

B．what is it

C．what it was

D．it what is

教材所介绍的调查方法中，有一种具体方法是与政治选举的预测一起发展起来的（）.

A.完全参与观察

B.半参与观察

C.非参与观察

D.抽样调查