2. Perhaps Catherine missed the bus - Perhaps Catherine could have missed the bus.
3. I'm sure Emma knew it was my birthday - I'm sure Emma must have known it was my birthday.
4. I'm sure Oliver didn't get the invitation - I'm sure Oliver can't have got the invitation.
5. I'm sure Matt went to the doctor's - I'm sure Matt must have gone to the doctor's.
6. I'm sure Richard didn't have a basketball match - I'm sure Richard can't have had a basketball match.
7. Perhaps Karen's car broke down - Perhaps Karen's car could broken down.