Сit may/could/must have been, etc complete the sentences. the second person agrees with the first. use might have, couldn't have, etc. ► matthew: i'm sure the computer didn't make a mistake. that's impossible. emma: no, of course the computer couldn't have made a mistake. 1 mark: i can't see the letter here now. so clearly someone posted it. alan: yes, 2 natasha: it's possible emma didn't hear the alarm. rachel: well, i suppose 3 sarah: henry drove at 100 miles an hour. don't you think that's dangerous? mark: yes, i 4 daniel: i just don't believe that andrew has failed the exam. vicky: andrew? impossible!
2 she may/might not have heard the alarm.
3 he shouldn't have driven at 100 miles an hour.
4 he can't/couldn't have failed the exam.