Choose the best meaning, A or B.

1 It must have been a wonderful party!
A I went to the party. B I didn’t go to the party.
2 Ellen can’t have been there.
A I’m sure about this. B I’m not sure about this.
3 Check your computer. They should have sent the email yesterday. A I think they sent an email. B I don’t think they sent an email.
4 That’s a pity. They might not have known about it.
A They didn’t know about it. B I don’t know whether they knew about it or not.