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