分类：教育/科学-学习帮助
问题：语法问题3请写出判断依据 
请写出判断依据
回答：选C。表示对过去所发生事情的肯定判断。

should have been 表示应该做但没有做的事情，含责备的意义。
You should have helped him.
He should have worked harder.

would have been 用于表示与过去事实相反的虚拟语气中。
Something must have happened or he would have been here 
then.
他肯定发生什么事了，要不然他早就到这里了。

could be 表示“有可能”，但可能性不大。
表示可能性概率的大小排列一般是must，can，could/ might