11. People ……must/mustn't……… stand on this bus.

12. You………mustn't…… cheat in a test.

13.We ……must……… do more exercise to stay fit.

14. You………mustn't…… turn the music too loud.

15. There ………mustn't…… be something wrong with the engine of this car.

16.You……must……… help in the house.

17. We ………mustn't…… give up when we are so close.

18. You………mustn't…… annoy your little sister.

19. This was a nice evening. We………must……meet again.

20. You……mustn't………bite nails.