问题补充:
Mr. Green has two sons, one of working as a bus driver now.
A. who
B. whom
C. them
D. whose
答案:
A. who
B. whom
(答案→)C. them
D. whose
解析:考查独立主格结构。根据one of working as a bus driver now中没有谓语动词可知不是从句,them指代前文提到的两个儿子,选项ABD一般用于引导定语从句,故选C。格林先生有两个儿子,他们其中一个现在做公交司机。