might /might have done 区别

might /might have done 区别
might可以表示对过去的猜测
might have done 也表示对过去的猜测
有何区别
3. Where did Adam get that new football?He hasn’t got any money.
It____a present.After all, it was his birthday last week.
A.might have been B.might be
可是答案选A

might have done 表示对过去所发生事情的推测,猜想 （注意Where did Adam get...的时态)
might 是may的过去式,表示比较委婉的“可能”,说话时间跟过去无关.