Question

【题目】Several weeks had gone by___he realized the painting was missing

A.as

B.before

C.since

D.when

Answer 1

【答案】B

【解析】句意：几个星期之后他才意识到那幅画丢了。as引导时间状语从句，表示两个动作同时发生。since自从，when当……时候，根据句意可将此三项排除。before可表示“……之后才……”