Here are the filled-in blanks for each statement using "if" or "unless":

1. Samantha’s parents won’t let her join the field trip **unless** she gets good marks.
2. **If** the festival attracts many tourists, it will create more jobs for the villagers.
3. **If** you keep eating too much fast food, you will get overweight.
4. We will arrive at the theatre 30 minutes late **unless** we go right now.
5. Visitors will have to drive on the left **if** they travel to Singapore.
6. The kid won’t get any new toys **unless** he learns to respect old people.
7. **If** the project succeeds, our traditional arts and crafts will be revived.
8. A musher will provide us with a dogsled ride **unless** there are special occasions, the tribes won’t perform the tribal dances.
9. They will try the street food at this night market **unless** they are still hungry.
10. You will experience playing the bagpipes **if** you travel to Scotland.
11. **If** the weather is bad, their wedding ceremony will be held in the county park.

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For section IX, here are the sentences using "if" or "unless":

1. If Katie visits Thanh Ha Pottery Village, she’ll make ceramic vase.
2. If that athlete donates his prize money to his home town, he will win the competition.
3. People will develop spine disorders unless they sit and walk properly.
4. I will walk around my neighborhood if I don’t have anything else to do.
5. Unless there is a storm, the tourists will go boating at Lake Tahoe.
6. The child will not be allowed to go out on Sunday unless he behaves better in class.
7. He will have a stomachache if he eats famous Italian blue cheese.
8. We won’t arrive on time for the opening ceremony unless we take the taxi.
9. If no one chooses this topic, those students will give a presentation on Mongolians.
10. Unless Martha learns English seriously, she won’t get the job she wants.