Mr. Smith is quite generous and warm-hearted a person you can turn when having trouble.A.

问题补充：

Mr. Smith is quite generous and warm-hearted, a person you can turn when having trouble.

A. for whom

B. with whom

C. to whom

D. of whom

答案：

A. for whom

B. with whom

(答案→)C. to whom

D. of whom

解析：句意：斯密斯先生是很大方和热心肠的人，一个你有麻烦可以求助的人。这里使用了定语从句，先行词是a person，定语从句中用的是turn to sb，所以填to whom，选C。