The doctorthe farmer sent his son is well-known in the field. A. by whomB. at whomC. to w

问题补充：

The doctorthe farmer sent his son is well-known in the field.

A. by whom

B. at whom

C. to whom

D. for whom

答案：

A. by whom

B. at whom

(答案→)C. to whom

D. for whom

解析：选C。考查定语从句。根据搭配send. . . to. . . 可知, 此处使用介词to, 故选C。