1. Switch phone off in class
Answer: (B) mustn't
Explanation: "Mustn't" is used to express a strong prohibition. Students are typically not allowed to have their phones switched on in class.

2. Help me clean the house
Answer: (B) Shall
Explanation: "Shall" is used in questions to make offers or suggestions, especially with "I" or "we". In this context, it's an offer to help.

3. Have any sweets
Answer: (A) mustn't
Explanation: "Mustn't" indicates that something is forbidden or not allowed, which makes sense if it's dinner time.

4. Wash the dishes yesterday
Answer: (B) didn't have to
Explanation: "Didn't have to" is used to express an absence of obligation in the past. It suggests the boys were not required to wash the dishes yesterday.

5. Come to the cinema
Answer: (A) Would
Explanation: "Would you like to..." is a polite way of making an invitation or offer.

6. Speak English when he was six
Answer: (C) could
Explanation: "Could" is the past tense of "can" and is used here to express an ability someone had in the past (when he was six).

7. Play football in the living room
Answer: (B) mustn't
Explanation: It is generally forbidden to play football inside the living room due to potential damage.

8. Open the door for me
Answer: (A) Would
Explanation: "Would you mind..." or "Would you..." are polite ways to make a request.

9. Go to school today. It's Sunday
Answer: (B) don't have to
Explanation: "Don't have to" expresses a lack of obligation. There is no requirement to go to school on a Sunday.

10. Carry those books for you
Answer: (C) Shall
Explanation: "Shall I..." is used to make an offer or suggestion.

11. Be careful when crossing the street
Answer: (B) must
Explanation: "Must" indicates a strong obligation or necessity to be careful for safety reasons.

12. Swim when I was two
Answer: (C) couldn't
Explanation: "Couldn't" is the past tense of "can't" and expresses an inability in the past. A two-year-old typically cannot swim.

13. A cup of tea
Answer: (A) Would
Explanation: "Would you like..." is a polite offer.

14. Use your laptop
Answer: (A) May
Explanation: "May I..." is a formal and polite way to ask for permission.

15. Go to the supermarket
Answer: (C) Could
Explanation: "Could I..." is a polite way to ask for permission or make a request.

16. The Wilsons buy a new car
Answer: (A) can't
Explanation: "Can't" expresses inability or impossibility. If it's too expensive, they are unable to buy it.

17. Go to bed late
Answer: (B) shouldn't
Explanation: "Shouldn't" is used to give advice or suggest that something is a bad idea. Going to bed late when you will be tired is not recommended.

18. Finish the test in an hour
Answer: (C) must
Explanation: "Must" indicates a strong obligation or rule that students have to follow.

19. Take a lunch break
Answer: (C) Could
Explanation: "Could I..." is a polite way to ask for permission.

20. Write an essay yesterday
Answer: (A) had to
Explanation: "Had to" is the past tense of "have to" and expresses an obligation in the past.

21. How I help you
Answer: (C) can
Explanation: "How can I help you?" is a common and polite phrase used to offer assistance.

22. See a doctor
Answer: (B) should
Explanation: "Should" is used to give advice. If someone looks ill, they are advised to see a doctor.

23. Go out tonight
Answer: (B) may
Explanation: "May" is used to express possibility or uncertainty about a future action.

24. Eat food in the library
Answer: (A) mustn't
Explanation: "Mustn't" indicates that something is forbidden, which is a common rule in a library.

25. Like some coffee
Answer: (C) Would
Explanation: "Would you like..." is a polite offer.