2021丽水专升本考试：英语4月每日一练4.27

1.hile he ______ his homework, his mother came in.

A. does

B. did

C. was doing

D. do

2.f the new safety system ______ to use, the accident would never have happened.

A. had been put

B. were put

C. should be put

D. would be put

【参考答案】

1【答案】C。解析：此题考查时间状语从句。while引导的时间状语从句，从句往往用进行时态。故选C。

2【答案】A。解析：根据句意可知，考查虚拟语气. 跟过去事实相反，从句用had done，主句用would have done，再结合new safety system 是被投入使用，故用had been done，即答案为A.