Question

The students _____ busily when Miss Brown went to get a book ____ in the office.

　 A. had written; left 　 B. were writing; has left

　 C. had written; had left 　 D. were writing; had left

 

Answer 1

D

 

第一个空表示动作正在进行；第二个空表示的动作发生在第一个动作之前。