Помогите с этим просто не понимаю! заранее спасибо!

1. Sam went to the party last weekend. 2. I could talk when I was three. 3. Mother wanted to buy a teddy bear for me. 4. You must study at school. 5. We should help our parents. 6. They travelled to the USA last year. 7. She moved to a new flat in 1995. 8. He sailed to America many years ago.  Вы не можете использовать "to" если у вас модальные глаголы, как: must, can/could, shall/should