问题补充：
The students busily when Miss Brown went to get the book she in the office.
A. were writing; left
B. wrote; had left
C. had written; left
D. were writing; had left
答案：
A. were writing; left
B. wrote; had left
C. had written; left
(答案→)D. were writing; had left
解析：状语从句（即when…）是过去时，主句动作和从句动作同时发生也应用过去时态，根据表达意义当老师进去时学生正在写，所以主句动作应该用过去正在进行时。she in the office这是定语从句，那本书是老师在取书之前放在办公室的，所以是动作发生在过去的过去，故第二空应该用过去完成时。
