4. "Why don't we go and have a look at the cathedral?"

-> He suggested going and having a look at the cathedral.

Cấu trúc: S + suggested + V_ing +...

5. The last time we met each other was ten years ago

-> We haven't met each other for ten years.

6. Unless we leave now we will miss the train.

Cấu trúc: Unless + S + V (simple present), S + will/can/shall + V

7.  My backpack is different from yours.

Cấu trúc: Different from SO or Sth.

=>
4. He suggested going and having a look at the cathedral./He suggested we should go and have a look at the cathedral.
-> suggest Ving : đề xuất, gợi ý
-> suggest S should V
5. We haven't met each other for ten years.
-> chuyển QKĐ sang HTHT, S have/has (not) V3/ed, for +khoảng thời gian
6. Unless we leave now, we will miss the train.
-> unless ~ if not
7. My backpack is different from your backpack.
-> different from : khác