1. Mary types letters in the office. => Letters is typed in the office by Mary. 2. His father will help you tomorrow. => You will be helped by his father tomorrow. 3. Science and technology have completely changed human life => Human life were completely changed by science and technology/ 4. Peter broke this bottle. => This bottle is broken by Peter. 5. They are learning English in the room. => English are being learnt in the room. 6. Nothing can change my mind. => My mind can't be changed. 7. No one had told me about it. => I hadn't been told about it. 8. I don’t know her telephone number => Her telephone number isn't known by me. 9. My students will bring the children home. => The children home will be brought by my students. 10. They sent me a present last week. => A present was sent me last week. GIẢI THÍCH CHO MÌNH CÁC CÂU NÀY