The opposite of happy is n happy. 2. He read the book twice. 3. She is a good (teach). 4. The meeting was a complete (fail). 5. It's very (help) to have a friend. 6. This problem is (solve). 7. He understood the instructions. 8. The (arrange) of the flowers was beautiful. 9. She is very (care). 10. The opposite of hopeful is hope 11. We need to build the bridge. 12. He was satisfied with the result. 13. I am (write) a letter right now. 14. The story was very (interest. 15. The building is under (construct). 16. She is a fast (run). 17. He made a (judge) about the situation. 18. It's (use) to buy this broken computer. 19. The food was (taste). 20. He is (think) about his future. 21. We are (plan) a trip to the beach. 22. The opposite of appear is dis 23. The (combine) of colors made beautiful art. 24. He paid the bill. 25. He was (lucky).

Here are the completed sentences with the correct forms of the words:

1. The opposite of happy is unhappy.
2. He read the book twice.
3. She is a good teacher.
4. The meeting was a complete failure.
5. It's very helpful to have a friend.
6. This problem is unsolved.
7. He misunderstood the instructions.
8. The arrangement of the flowers was beautiful.
9. She is very careful.
10. The opposite of hopeful is hopeless.
11. We need to build the bridge.
12. He was unsatisfied with the result.
13. I am writing a letter right now.
14. The story was very interesting.
15. The building is under construction.
16. She is a fast runner.
17. He made a judgment about the situation.
18. It's useless to buy this broken computer.
19. The food was tasty.
20. He is thinking about his future.
21. We are planning a trip to the beach.
22. The opposite of appear is disappear.
23. The combination of colors made beautiful art.
24. He promptly paid the bill.
25. He was unlucky.

Let me know if you need further assistance!