1. I can't send her a postcard because I don't know her address => If
2. Ann has a bad cold, so she can't go to the circus today => If
3. They don't clean the window that's why the room looks rather dark
=>If
4. Sue was ill, so she couldn't go to the party
=> If
5. They didn't have enough money therefore, they didn't buy the bigger house
=> If
6. Mary was not injured in the crash because she was wearing a seat belt => If
7. The bus didn't stop because you didn't put your hand up
=> If
1 if i had known her address, i could have sent her a postcard
1If I knew her address, I could send her a postcard
2If Ann hadn't have a bad cold, she could go to the circus today
3If they cleaned the window, the room wouldn't look rather dark
4If sue wasn't ill, she could go to the party
5If they had enough money therefore, they would buy the bigger house
6If Mary wasn't wearing a seat belt, she would be injured
7If you put your hand up, the bus would stop