I don't know when she ---,but when she----,i -----you know.

问题描述:

I don't know when she ---,but when she----,i -----you know.
a.comes ,will come ,let b.will come,comes ,will let c.will come ,comes ,let d.comes ,comes,let

b.will come,comes ,will let 是正确的答案.
will come是宾语从句部分.comes --主将从现中的现.will let ----主将从现中的将.为什么不可以选另外的三个?另外三个是什么意思呢?谢谢因为不符合主将从现的原则,或者时态混乱。