Câu điều kiện loại 2: 

If + S + V-ed/V2, S  + would/could/should... + V-inf

Câu điều kiện loại 3:

If + S + had + Vpp/V-ed, S  + would/could/might + have + Vpp/V-ed

16. If it hadn't snowd so much yesterday, I could have gone out.

17. If Mary had gone to the disco, I could have seen her.

18. If it hadn't rained, the football match wouldn't have been cancelled.

19. If I were over 18. I could go to the disco.

20. If I had had enough money. I could have bought a new mobile phone.

$16.$ If it hadn't snowed so much yesterday, I could have gone out.

$17.$ If Mary had gone to the disco, I would have seen her.

$18.$ If it hadn't rained, the football match wouldn't have been canceled.

$19.$ If I were over 18, I could go to the disco.

$20.$ If I had had enough money, I could have bought a new mobile phone.

$=========="$

- Câu điều kiện loại $II$ (Câu $19$): If + S + Thì quá khứ đơn , S + would/ could/ might + V (Bare).

  + Nói về một sự việc không có thật, không thể xảy ra ở hiện tại.

- Câu điều kiện loại $III$ (Câu 16, 17, 18, 20):  If + S + Thì quá khứ hoàn thành, S + would/ could + have + V (Pii).

   + Dùng để nói về một sự việc không có thật trong quá khứ, bày tỏ sự tiếc nuối trong quá khứ.