问题
选择题
Helen ______ her keys in the office so she had to wait until her husband ______ home.
A．has left; comes
B．left; had come
C．had left; came
D．had left; would come
答案
答案：C
考察时态。根据句意可知，Helen因为先把钥匙丢在了办公室，所以她要等她的丈夫回家。
所以leave发生在had to wait之前，即过去的过去，用过去完成时，第二空是until引导的时间状语从句，从句中用一般过去时表示过去将来。