`1.` If he didn't have to study for his exam, he could go out.

`2.` If she weren't lazy, she could pass the exam.

`3.` If he didn't smoke so much, he could get rid of his cough.

`4.` If I didn't feel tired, I could play football this afternoon.

`5.` If Olga and Ivan had been paying attention, they would have seen the sign marking their exit from the highway.

`6.` If she had a college degree, she could be employed.

`7.` If she hadn't walked to the meeting, she wouldn't have been late.

`8.` If you don't promise to return back, I won't lend you.

`9.` If the weather hadn't been terrible, we wouldn't have put off our trip.

`10.` If Sally hadn't been absent from school on Friday, she would know what she has to do for homework.

`11.` Unless you like this one, I'll bring you another.

`12.` But for being very nervous, Martin wouldn't have failed his driving test last week.

`-` But for + N/V_ing, S + would have + V_ed/3

`13.` If he pays me tonight, I will have enough money to buy a car.

`14.` If you don't leave me alone, I'll call the police.

`15.` Should you arrive at the office earlier than I do, please turn on the air-conditioner.

`16.` Had it not been for his early death, he would be a famous musician by now.

`17.` Were you to take good care of the car, it wouldn't break down so often.

`18.` If you tell lies to your boss, you'll be fired at once.

`19.` Had he revised all his lessons, he wouldn't have failed the exam.

`20.` If Rita had got some sleep last night, she wouldn't be exhausted today.

`-----------------------`

`@` If type 1 : If + S + V_s/es/inf, S + will/can + V_inf

`->` diễn tả sự việc có thể xảy ra, dự đoán

`-` Đảo ngữ : Should + S + V, S + will/can/may + V_inf                          

`-` Unless + S + V_s/es/inf , S + will + V               

`@` If type 2 : If + S + V_ed/2, S + would/could + V_inf

`->` diễn tả tình huống ko có thật ở hiện tại              

`-` Đảo ngữ : Were + S + to V, S + would/could/might + V_inf

`@` If type 3 : If + S + had + V_ed/3, S + would/could + have + V_ed/3

`->` diễn tả tình huống đã ko xảy ra trong quá khứ

`-` Đảo ngữ : Had + S + V_ed/3, S + would have + V_ed/3