i got up early that morning,but i__so because i had no work to do.

问题描述:

i got up early that morning,but i__so because i had no work to do.
A.mustn't have done B.didn't need to do C.needn't have done D.must have to study
B为什么不对

因为后面有"because I had no .."
所以前后还有时间上的距离,即我起床,然后没有事情做
因此要用完成时态