The old man has three sons and two are doctorsA. of whichB. of whomC. of themD. of that

问题补充：

The old man has three sons，and two are doctors．

A. of which

B. of whom

C. of them

D. of that

答案：

A. of which

B. of whom

(答案→)C. of them

D. of that

解析：考查代词。根据句中连词and可知，后面连接并列分句，非考查定语从句，故用代词them，指代three sons。句意：老人又3个儿子，2个是医生。