should 与 might 的区别?

题目

should 与 might 的区别?
Since this is the first time he has made such a mistake,___forgive him
A.could as well B.can as well C.should as well D.might as well
为什么答案是D,从词面上来说C选项不是也可以么?求解,谢谢

答案

might as well是固定搭配,意思是“不妨”语气较弱,而should as well 不是固定搭配,should 语气较强,意思是“应该”