he introduced me to a friend from America------he had often mentioned.

题目

he introduced me to a friend from America------he had often mentioned.
a about whom b who c which d about which 为什么选b,who在从句中有不是作主语,

答案

B.who在定语从句中可以作主语或宾语;而在句子中mention是及物动词,所以mention后可以直接加宾语,即选who.
太荒唐了,楼上的即使是从句却状语,who又怎么能够作状语?