做题目遇见几个问题，请教高手1、The best thing______happened to me was findi

做题目遇见几个问题，请教高手
1、The best thing______happened to me was finding my best friend,Tom
A.what B.as C.that D.which
正确答案是什么？为什么不选D 请详细解释一下
2._______,I went back to my dormitory unhappy in the eveing
A.With antthing done B. with somthing doing
C.with nothing done D.with noting having done
选什么？为什么？