有关情态动词表推测的问题
例1：Conserding his ability and experience,he ____ better.
A.can have done
B.might have done
应该选B,老师说没有can have done,因为can表能力时有时态区别,所以只有could have done,但有can't have done,这是can表推测,没有时态区别.（说的对吗?）
但这里用might,might不也表推测吗?为什么不能是选A,can表推测?难道can只能做否定推测以及客观推测?
还有,关于should的用法,should也可表推测吧,“他应该是最高的孩子”应该是什么?“He may be the tallest boy.”should can行吗?并请给出解释.
例2.-I can't find my purse.
-You ___ have lost it while shopping.
A.may B.can C.should
其他两个为什么不行呢?