Sure! Here are the best options for each blank in the provided sentences:

12. She is **A. keen** of taking photos.
13. Mai is **B. interested** in history.
14. My sister is **C. fond** of cooking.
15. My brother spends lots of time **B. to surf/into** the net but I am not **C. fond** of it.
16. I am not **A. keen** about doing DIY.
17. You should avoid **C. watching** too much TV. It's not good for your eyes.
18. Lan used to love **A. using** in front of the computer for hours but now she doesn't. She takes part in a judo club.
19. Minh is a very hard-working boy. He doesn't mind **D. doing** a lot of homework in the evenings.
20. Do you fancy **A. going** around the West Lake with me this Sunday morning?
21. Trang: What do you do in your free time? Tom: I’m a bit different. I usually **A. hang out** with my friends.
22. Why don't we **B. invite** our parents with some DIY projects? I think it is useful.
23. My baby: **A. help**.
24. My dad doesn't mind **B. picked up**.
25. Tom: What are you doing? Trang: I am looking **C. for** a knitting kit.
26. Doing origami helps me **A. relax**.

For Question 4, you would rewrite the sentences using the specified format.

For Question 5, here are the completions:

1. She loves making models. -> She is **fond of** making models.
2. He dislikes doing the washing-up. -> He doesn’t **enjoy** doing the washing-up.
3. It takes him 3 days to do that model. -> He is **interested in** doing that model.
4. It took her a week to build that dollhouse. -> She is **crazy about** building that dollhouse.

Let me know if you need any further assistance!