Ответ:

36. Tim should go to the dentist because he has a toothache.

37. Negative: We don't have to take chairs to the concert.

Interrogative: Do we have to take chairs to the concert?

38. Negative: He doesn't have to do his homework every day.

Interrogative: Does he have to do his homework every day?

39. Negative: You shouldn't eat fruit and vegetables.

Interrogative: Should you eat fruit and vegetables?

40. Negative: I can’t dance very well.

Interrogative: Can I dance very well?