【题目】A good friend is a person________ we tum for help when we are in trouble.
A.who
B.whom
C.to whom
D.to which

【答案】C
【解析】考查定语从句。句义：朋友是你处于困境时可以求救的的人。turn to sb固定短语,“向某人求救”，所以用介词to ,因为先行词是a person,是人所以用whom，所以C正确。