Question

The professor said he could talk on _____ interested the audience.

1. A.
   any topic
2. B.
   which topic
3. C.
   whichever topic
4. D.
   the topic he thought it

Answer 1

C
whichever已失去疑问含义，等于 anything that，表示强调；而 which topic中 which保留疑问含义，译成"哪一个题目"，不符合句义。而A和D中缺少连词。