1. We haven't seen him on Monday. 

2. If you don't work hard, you will fail the exams. ( câu điều kiện sự thật hiển nhiên dùng câu đk loại 1: If + S + V ,S+ will + V ....)

3. We haven't seen our grandfathers for 2 years. (2 years ago chuyển HTHT-> for 2 years)

4. If I had a car, I could give you a lift. ( câu điều kiện giả định một việc gì đó dùng câu đk loại 2  :          If+S+Ved,S+would/could... +V...) 

5. If I didn't live far from school, I wouldn't have to cycle to school every day. (như câu4)

Chúc bạn học tốt 

1)We haven't seen him since Monday

2)if you don't work hard , you will fail the exam

3)We haven't seen your grandfather for two years

4)if i had a car ,i could give you a lift

5)If I didn't live far from school ,I wouldn't have to cycle to school every day

Chúc bn hc tốt ^^