When I try to find that prevents so many people from taking part in the program it seems

问题补充：

When I try to find that prevents so many people from taking part in the program,it seems to me that there are two main causes.

A. why it does

B. what it does

C. what it is

D. why it is

答案：

A. why it does

B. what it does

(答案→)C. what it is

D. why it is

解析：find后为一个宾语从句，而且这个从句为强调结构。全句的意思是“当我想努力找出阻止许多人参加这一节目是什么原因时，依我看似乎有两个理由”。