I'll help you when I _____ my work .

问题描述:

I'll help you when I _____ my work .
A. finishedB. will finish
C. have finishedD. had finished
这句答案是选B,请问为什么?我觉得这个句子应该是主将从现的句子,可怎么没有现在时的选项呢?

时间状语从句一大原则:主将从现(主句将来时,从句现在时)
所以这里答案可以是:finish 或have finished
have finished 强调完成之后 故这里选C