=>
1. We haven't seen Mr. Pike for nearly four years.
-> chuyển QKĐ sang HTHT, S have/has (not) V3/ed, for + khoảng thời gian
2. People recycle old car tires to make shoes and sandals.
-> chuyển bị động HTĐ sang chủ động : S Vs/es
3. It's very necessary to keep our environment clean.
-> it's adj to V
4. Trang (My sister) used to learn harder than she does now.
-> used to V : đã từng
5. The doctor advised Mr. Hoang to take more exercise.
-> advise sb to V : khuyên ai làm gì