1: I don't know his number, so I don't phone him
If.......................................................................
2: He doesn't invite me to his birthday party, so I can't come there
If.......................................................................
3: The motor is expensive, so I can't affort it
If........................................................................
4: I have to work tomorrow evening, so I can't meet you
If........................................................................
5: We don't visit you very often because you live so far away
If........................................................................
6: Because he doesn't understand the lesson he can't do the exercise
If........................................................................
7: She studies very hard so her parents are proud of her
If.......................................................................
8: He doesn't speak very clearly, that's why people don't understand him
If......................................................................