---How is that,Joan?---Yeah,it's from the boss.She ( ) first

---How is that,Joan?---Yeah,it's from the boss.She ( ) first whether she likes it.
A．shall go
B.ought to have gone
C.should go
D.must have go
请讲详细点选哪个
还有为什么不能选C
AC应该都可以表“应该”嘛
但麻烦讲一下为什么不选其他的，THANKS!
还有could have done和might have done都有本可以做而没做成的意思，那么二者有什么区别呢？
比如这个题
---John saw a three-year-old cjild walking alone in a sjopping mall,so he took the child home immediately and called the police.
---But he_____have waited withthe child until the parents returned.
A.shouldn't B.could C.would D.might
为什么选B而不选D呢？
再次THANK YOU ALL!