The visiting professor gave us some advice of great help to our English learning.A. I t

问题补充：

The visiting professor gave us some advice, of great help to our English learning.

A. I think it is

B. I think which is

C. which I think is

D. which I think it is

答案：

A. I think it is

B. I think which is

(答案→)C. which I think is

D. which I think it is

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