Mrs. Smith locked both the front

Mrs. Smith locked both the front and the back doors before went to bed _______ that someone might steal into the house at night.
A、so
B、for fear
C、unless
D、on condition
【正确答案】：B
【题目解析】：译文：史密斯夫人在上床休息之前总是将前后门紧锁，以防有人晚上进来偷东西。四个选项中，so指"因此"，引导一个句子；for fear指“以防”；unless指“除非”；on condition指“条件是"。根据句意，for fear最符合题意。答案为B。