Ответ:

1 Ross didn’t know Paula’s number, so he didn’t ring her.

If Ross had known Paula’s number, he would have rung her.

2 I had an accident because I didn’t drive carefully.

I wouldn't have had an accident if I had driven carefully.

3 Annie and Martin were late for school because they missed the bus.

Annie and Martin wouldn't have been late for school if  they hadn't missed the bus.

4 Jake and Rachel had a big fight, so they split up.

If Jake and Rachel hadn't had a big fight, they wouldn't have split up.

5 Your dad was disappointed because you forgot his birthday.

Your dad wouldn't have been   disappointed if you hadn't forgotten his birthday.

6 I didn’t train hard, so I didn’t win the competition.

If I had trained hard, I would have won   the competition.

7 My girlfriend was angry because I lied to her.

My girlfriend wouldn't have been angry if I hadn't lied to her.

8 We didn’t have enough money, so we couldn’t buy a new laptop.

If we had had enough money , we could have bought a new laptop.

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