Question

I ________ for three hours when I suddenly became sick．

1. A.
   had been working
2. B.
   would work
3. C.
   have worked
4. D.
   am working

Answer 1

A
句意是“我一直工作了三小时，这时我突然觉得不舒服”。此处要用过去进行时表示到过去某个时间为止一直持续的状态。