---You could have asked your teacher for help .He

问题补充：

---You could have asked your teacher for help .He is kind-hearted .---Yes,a whole day

答案：

C,could have done 表示本能做某事,但实际上却没有做,所以这应该是一个完成时态,但是时间是被浪费掉,是被动语态,所以选C.

======以下答案可供参考======

供参考答案1:

C供参考答案2:

C