Ответ:

  1. My brother was eating when I arrived.
    Мой брат ел, когда я пришёл.
  2. While my friend was listening to music, I was sleeping.
    Пока мой друг слушал музыку, я спал.
  3. As they were walking to school, a bus drove past.
    Когда они шли в школу, мимо проехал автобус.
  4. My mum was reading while my dad was cooking dinner.
    Моя мама читала, пока папа готовил ужин.