Mr. Green has two sons one of working as a bus driver now.A. whoB. whomC. themD. whose

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。