Bài 1: Choose the correct answer (mustn't or needn't). 1. Mary___________ go to bed early because tomorrow is her day off. 2. You___________ smoke on the bus. It's forbidden. 3. You ___________ do it now; you can finish it later. 4. Students_____________use their mobile phones during the test. 5. You____________buy any beef. There is plenty of it in the fridge. 6. You____________bring an umbrella. I can lend you one. 7. It's a secret. You____________tell anybody. 8. You____________do the washing up as we have a dishwasher. 9. You really ____________be late again. 10. You______drink at all if you plan to drive.