"any topic" or "whichever topic"

[xxwzs]

Here presented a test question from China's College Entrance Exam.

The professor said he could talk on _____ interested the audience.
A. any topic B. which topic
C. whichever topic D. the topic he thought it

1. Answer C is specified as the standard one, why?
2. According to my knowledge, I would like to adjust this sentence into "The professor said he could talk on any topic interesting the audience." or "The professor said he could talk on any topic which interested the audience." Are my sentences correct?

 

[bhaisahab]

Of the available options the only one possible is C.

 

[MikeNewYork]

I agree that C is correct. Your second example is correct. I find your first sentence to be a bit strange.

 

[Tdol]

Strange, but not incorrect. I would go for the second, which could also use any topic that interested the audience.

 

[emsr2d2]

Here presented a test question from China's College Entrance Exam.

I think this is the sentence MikeNewYork found strange, as do I.

 

[Tdol]

I thought Mike was referring to "The professor said he could talk on any topic interesting the audience."

 

[MikeNewYork]

Well, I wasn't thrilled with that one either.