There are many new central leaders in China now many once worked in the western provinc

问题补充：

There are many new central leaders in China now, many once worked in the western provinces.

A. in which

B. of whom

C. in whom

D. for whom

答案：

A. in which

(答案→)B. of whom

C. in whom

D. for whom

解析：B句意：如今在中国出现了许多新的中央领导人，他们中许多人都曾在西部省份工作。先行词是人，应用关系词whom引导定语从句；表所属，应用of。