Ответ:

  1. Jack, please clean up your room by yourself.
  2. Did she draw this beautiful picture by herself?
  3. This trip could be dangerous, take care of yourself!
  4. When my brother was 3 years old he couldn’t do anything by himself.
  5. Yesterday I hurt myself when I was riding a bike.
  6. They are good cooks. They can cook everything by themselves.
  7. We arranged for Frankie’s birthday party by ourselves.
  8. Do you need my help? — No, thank you. I’ll do it myself.