Here are the correct answers for each sentence:

21. **C. of** (Jack and Janes are interested in doing puzzle.)
22. **C. interested** (My sister is interested in cooking. She wants to become a chef in the future.)
23. **B. visited** (They visited Ho Chi Minh City last summer.)
24. **C. On** (On Friday morning, there is a meeting between 11 am and 1 pm.)
25. **A. at** (My sister is very fond at eating chocolate candy.)
26. **C. talking** (I always enjoy talking to my grandfather. He always tells me great stories.)
27. **B. to driving** (Nam dislikes driving, so he never drives to work.)
28. **C. to play** (Jane prefers to play music to listening to it.)
29. **B. on** (The final examination will be held on June 9th, 2023.)
30. **C. making** (My grandma enjoys making woolly hats in her free time.)

Please let me know if you need further assistance!