Ответ:

Краткое пояснение:

Краткое пояснение: Необходимо исправить грамматические ошибки в предложениях, связанные с использованием модальных глаголов и других грамматических конструкций.

Пошаговое решение:

  1. 1. Children under 15 must to go to school.
    Children under 15 must go to school.
  2. 2. This exercise is optional - you mustn't do it.
    This exercise is optional - you don't have to do it.
  3. 3. If you have to doing it now, I'll help you.
    If you have to do it now, I'll help you.
  4. 4. You don't have to open the car door when the car is moving.
    You mustn't open the car door when the car is moving.
  5. 5. I don't think you must go to bed very late.
    I don't think you should go to bed very late.