I really can’t decide first. A small computer or a big one?A. what to buy B. to buy whatC

问题补充：

I really can’t decide first. A small computer or a big one?

A. what to buy

B. to buy what

C. which to buy

D. to buy which

答案：

A. what to buy

B. to buy what

(答案→)C. which to buy

D. to buy which

解析：在两种中选择，用which。