Complete the sentences with the appropriate form of the words in parentheses. Add not if necessary for a sentence to make sense.
1. could be visiting
2. should watch
3. must have thrown
4. should be working ....shouldn't be wasting
5. must be playing
6. might be taking
7. should have bought....shouldn't have waited
8. must have been driving
9. must not have planned
10. may have borrowed....couldn't have borrowed
11. could not have been listening
12. couldn't have told
13. must not have....must have been sleeping
14. must be making
(Tư liệu tham khảo: Betty Schrampfer Azar. Understanding and Using English Grammar.3rd ed)

Review exercise