`1.` He used to spend the evening in the library.

`-` S + used + to V-inf : đã từng làm gì trong quá khứ

`2.` Lan didn't go to school last Friday because she was sick.

`-` Because + MĐ nguyên nhân : bởi vì

`3.` Vietnam, which is in the south-east Asia, exports a lot of rice, coffee, and rubber.

`-` Which thay thế N chỉ vật , làm chủ ngữ / tân ngữ trong câu ( có thể đứng sau giới từ )

`4.` I revise quickly my lessons again before breakfast.

`-` revise sth again : ôn lại điều gì

`5.` We won't survive unless we start working on cleaner and safer sources of energy.

`-` Unless `=` if not : nếu không