1. It must be a terrific film if Kate has seen it four times. b) probability
2. Sorry, I must leave a little earlier today. a) obligation
3. You mustn't tell anyone about this - it's a secret. c) prohibition
4. Must I take this medicine: it has a bitter taste! a) obligation
5. They must be having a wonderful time at the seaside. b) probability
6. Kids mustn't get smart aleck with grown-ups. c) prohibition
7. London must be bigger than Paris. b) probability