12、It had begun before my sister left. My sister left _________it had begun.
A.behind
B.before
C.without
D.after
标准答案:D.after
解析:after引导it had begun作为时间状语从句出现在这个句子里
而且从时态上讲, my sister left是一般过去时
after it have begun是在它开始之后
所以”它”在我姐姐离开之前就开始了, 过去的过去, 用过去完成时,