1. Keep silent or you'll wake up the baby.
-> If you don't keep silent, you'll wake up the baby.
2. Because you don't leave immediately, I call a policeman.
-> If you left immediately, I wouldn't call a policeman.
3. I don't know her number, so I don't ring her up.
-> If I knew her number, I would ring her up.
4. Go right now or you'll be late for the train.
-> If you don't go right now, you'll be late for the train.
5. As she is often absent from class, she can't keep pace with her classmate.
-> If she weren't often absent from class, she could keep pace with her classmates.
6. I couldn't write to Alice because I didn't know her address.
-> If I had known her address, I could have written to Alice.
7. I don't know the answer, so I can't tell you.
-> If I knew the answer, I could tell you.
8. We got lost because we didn't have a map.
-> If we had had a map, we wouldn't have got lost.
9. His friends werre so late, so they missed the train.
-> If his friends hadn't been so late, they wouldn't have missed the train.
10. today isn't Sunday, so the pupils can't go swimming.
-> If today were Sunday, the pupils could go swimming.