When I tried to find that prevented so many people from taking part in the program it see

问题补充：

When I tried to find that prevented so many people from taking part in the program, it seemed to me that there were two main reasons.

A. why it did

B. that it did

C. what it was

D. why it was

答案：

A. why it did

B. that it did

(答案→)C. what it was

D. why it was

解析：本题是强调句和宾语从句的考查。宾语从句缺少主语，用what。强调句中强调部分为疑问副词应提前，故选C项。