Must have, could have 1. The door was locked, but the thief managed to get into the hotel room. He might have had a key. He may have known how to open the door. He must have been professional. He might have already committed a robbery. 2. Mr. and Mrs. Sullivan are very worried. Their daughter usually gets home from school at 4.30. It's 6 o'clock and she hasn't arrived yet. She might have gone to the cinema with friends. She must have had some problems. She can't have been at school. She may not have called to her family. She might have gone out from her family with her boyfriend. 3. Neil phoned his boss at 9 o'clock and said he was too ill to come to work. At 9.30 his boss phoned his house, and there was no reply. Neil must have slept and hadn't listened that phone call. Neil might not have been ill. Neil could have been in a bathroom. Neil must have gone to a hospital. 4. Gregg made a date with Penny. They arranged to meet outside the cinema at 7.30. It's 8 o'clock and she hasn't turned out. Penny must have been in troubles. Penny must have been in traffic. Penny can't have forgotten about the date. Penny might have been late at work. Penny may not have gone to other country.