1. I am sorry i disturbed you. I did not know you were busy → If.... 2. It might rain. if it does, everyone can eat inside → If.... 3. Margaret was not injured in the crash because she was wearing a seat belt. → If.... 4. I have to work tomorrow evening, so i can not meet you → If....

1. I am sorry i disturbed you. I did not know you were busy

→ If....I had known you were busy, I wouldn't have disturbed you

2. It might rain. if it does, everyone can eat inside

→ If....it rains, everyone can eat inside

3. Margaret was not injured in the crash because she was wearing a seat belt.

→ If....Margaret had been wearing a seat belt, he wouldn't have been injured in the crash

4. I have to work tomorrow evening, so i can not meet you

→ If..I didn't have ..to work tomorrow evening, I could  meet you