- 3 câu khẳng định là : 
+ You must study for the exam if you want to pass.
+ We must arrive at the airport early to catch our flight.
+ He must eat a healthy diet to maintain his weight.

- 3 câu phủ định là :
+ You mustn't forget to lock the door when you leave the house.
+ We mustn't waste water during the drought.
+ She mustn't drive without a valid driver's license.