Here are the completed sentences using the structure "if + Present Simple, S + will/won't":

1. If **the weather is** beautiful tomorrow, **we will drive** to the beach.
2. If **she sends** the letter now, **they will receive** it tomorrow.
3. If **Fred is** angry if **Jack arrives** late again.
4. If **I come** to your house if **I have** enough time.
5. If **she doesn't pass** this exam, **she won't get** the job that she wants.
6. If **you learn** a lot if **you take** this course.
7. If **I get** a ticket, **I will go** to the cinema.
8. If **I buy** that machine if **it doesn't cost** too much.
9. If **you run** very fast, **you will catch** the taxi.
10. If **I go** to the doctor's if **I don't feel** better tomorrow.
11. If **they win** this match, **they will be** the champions.
12. If **it rains**, **we won't go** fishing.