Question

When I came in, he ______.

A. is helping Tom mend the clock

B.was helping Tom mending the clock

C.is helping Tom mends the clock

D.was helping Tom mend the clock

 

Answer 1

答案：D
解析：

因为时间状语从句为一般过去时，所以主句要用过去的某种时态；而help后面要跟动词原形，故选D。