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1. If he didn't smoke too much, he could get rid of his cough.

2. If there weren't gravity, water couldn't run down hill. 

3. If she had taken her friends' advice, she wouldn't have failed in her business.

4. If Dick didn't drive carelessly, he wouldn't often cause accidents.

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

6. If he took some exercises, he wouldn't be unhealthy.

7. If you don't study hard, you won't pass the exam.

8. If he had revised all his lessons, he wouldn't have failed the exam.

9. If it rains, we'll stay at home.

10. If I hadn't lost my watch, we wouldn't have missed our plane when we went on holiday.

1. He smokes too much; that's why he can't get rid of
his cough.

$\to$ If he didn't smoke too much, he could get rid of his cough.
2. Without gravity, water couldn't run downhill.

$\to$ If there weren't gravity, water couldn't run downhill.
3. She didn't take her friends' advice; therefore, she
failed in her business.

$\to$ If she had taken her friends' advice, she wouldn't have failed in her business.
4. Dick often causes accidents because he drives
carelessly.

$\to$ If Dick drove carefully, he wouldn't cause any accidents.
5. He will pay me tonight. I will have enough money
to buy a car.

$\to$ If he pays me tonight, I will have enough money to buy a car.
6. He doesn't take any exercises. He is so unhealthy.

$\to$ If he took some exercises, he would be healthy.
7. Study hard, or you won't pass the exam.

$\to$ If you study hard, you will pass the exam.
8. He didn't revise all his lessons. He failed the
exam.

$\to$ If he had revised all his lessons, he wouldn't have failed the exam.
9. In case it rains, we'll stay at home.

$\to$ If it rains, we'll stay at home.
10. I lost my watch and, as a result, we missed our
plane when we went on holidays.

$\to$ If I hadn't lost my watch, we wouldn't have missed our plane when we went on holidays.