seems to be a strong competition in China for senior high students to enter universities

问题补充：

seems to be a strong competition in China for senior high students to enter universities does exist in other countries as well.

A. It

B. Which

C. What

D. That

答案：

A. It

B. Which

(答案→)C. What

D. That

解析：在这个主语从句中，设空处作主语，故用what。