Alec asked the policeman ________ he worked to contact him whenever there was an accident．

A.with him

B.who

C.with whom

D.whom

答案及解析： C

解析：

该句主要说明Alec asked the policeman to contact him whenever there was an accident，其中的he worked部分显然为定语从句修饰the policeman，A项没有起引导作用的词，应排除；

work with sb．指“与某人共事”，缺少介词with的B、D项应排除。该定语从句是由“介词+whom”引导的。