问题补充：
I have many friends, some are businessmen.
A. of them
B. from which
C. who of
D. of whom
答案：
A. of them
B. from which
C. who of
(答案→)D. of whom
解析：此题考查学生对定语从句的掌握和运用能力。此题属于“of+关系代词+部分(指物用which；指人用whom)” 引导定语从句。该从句可改写为: some of whom are businessmen.
