EX 1:

1. Lan can play badminton on Sungays but she must do housework first. 

2. Ba can watch TV in the evening but he must go to bed early.

3. Tuan can listen to music with his stereo but he must keep the volume down.

4. Lan can go out with her friends on Sunday but she must help her mother in the kitchen first.

5. Hoa can stay up late at Saturday night but she must get up before seven.

EX 2:

1. We are too young, so we must not ride a motorbike.

2. The traffic lights are green, must not cross the street. 

3. It is stop sign, we must not go straight on.

4. Roads are dangerous, must not ignore the road signs.

5. There is an intersection ahead, must not go fast.

EX 3:

1. I can swim. I go swimming every week.

2. The traffic lights are red. You must stop.

3. The cars go very fast. We must be careful. 

4. You can't play in the street.

5. My brother can't drive a car. He is very young.

6. The students must do their homework.

7. There is a "No Parking" here. You mustn't park your car here.

8. This sign says "Stop." We must stop.

9. Our roads are dangerous place. We must have discipline.

10. We must not you fast.

I.

1. Loan can play badminton but she must do homework first.

2. Ba can watch TV in the evening but he must go bed early.

3. Tuan can listen to music his stereo but he must he keep volume down.

4. Lan can go out with friends on Sunday but she must but she must help mother first.

5. Hoa can stay up late on Saturday but she must get up before seven.

II.

1. We are too young, must not ride motorbike.

2. Traffic lights green, must not cross the street.

3. It stop sign, must not go straight on.

4. Road dangerous, must not ignore road signs.

5. There is intersection ahead, must not go fast.

III.

1. can

2. must

3. must

4. mustn't

5. can't

6. must

7. mustn't

8. must

9. must

10. must