Alec asked the policeman ________ he worked to contact him whenever there was an accident．
A.with himB.whoC.with whomD.whom在线课程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。