1,1, I last saw him when I was a student

→→ S + have/has + not + P2 + ... + since + t/gian

== S + last + V2/ed + ... + when + t/gian

2,2, I haven't played football since 19701970

→→ The last time + S + V2/ed + ... + was + t/gian

== S + have/has + not + P2 + ... + since/for + t/gian

3,3, If she was on board now, she could experience these marvelous things

→→ Động từ chia ở thì hiện tại →→ chuyển sang câu điều kiện loại 33

→→ ĐK loại 22: If + S + V-qkđ, S + would/could/should + Vbare-inf ...

→→ Điều kiện không có thật ở hiện tại

4,4, If you don't work hard, your parents will be sad

→→ ĐK loại 11 : If + S + V-htđ, S + will/can/shall + Vbare-inf ...

→→ Điều kiện có thể xảy ra ở hiện tại hoặc tương lai

• I last saw him when I was a student.
• I haven't played football since 1970.
• If she were on board now, she could experience these marvelous things.
• If you don't work hard, your parents will be sad.