Question

I didn't manage to do it _____ you had explained how. A. until B. since C. while D. after

答案是A，但是explain这个动作不是发生在didn't manage 之后吗？怎么能用过去完成时？

Answer 1

选D. after。 从时态可以分析出来。
you had explained how 过去完成时，
I didn't manage to do it 过去时。 过去完成时 是过去的过去发生的，即you had explained how 要发生在I didn't manage to do it 之前， 所以选择after。