Question

I ________ my key to my office at home, so I had to wait until other teachers ________ to open the door．

1. A.
   had left; came
2. B.
   left; came
3. C.
   has left; came
4. D.
   left; would come

Answer 1

A
本题考查过去完成时和一般过去时的比较。leave my key这个动作明显发生在had to wait之前，所以为过去的过去，用过去完成时；而come这个动作是出现在until引起的时间状语从句中，应该用一般过去时代替过去将来时，所以答案为A项。