问题补充:
He has three children, are doctors.
A. and two of whom
B. two of them
C. two of whom
D. two of which
答案:
A. and two of whom
B. two of them
(答案→)C. two of whom
D. two of which
解析:这题考查句子结构,因为先行词是children,定语从句要用whom,如果是and连接的并列句,要用and two of them,所以选C。