1.Why isn039;t Ann in class today. She___ sick. We don039;t know

1.Why isn't Ann in class today. She___ sick. We don't know anything about her.
a) might/may
b)should
c)would

2.What are you doing next week? I ____ be in the mountains.
a)should
b)may/might
c)can

3.You want to give your friend a piece of advice. He is not good at English. "You ______ regularly work hard at your English".
a)could
b)may
c)should

4.Your friend hasn't learnt the new words of this unit. He wants you to translate them but you say that she/he _____ learnt the new words yesterday.
a)should have learnt
b)might have learnt
c)can learn

5.A sheet of your text book is missing. You don't think that your little brother has torn it. (you don't belive it). He ___ the sheet of the text book.
a)shouldn't tear
b)couldn't have torn
c)didn't have torn.