Here are the corrections for the sentences provided in the exercise:

4. **Corrected:** Linda wishes she had a new smartphone and a new bike.
5. **Corrected:** I want to observe the changing colours of the leaves in autumn.
6. **Corrected:** I was waiting for the bus when I realized I had forgotten my umbrella.
7. **Corrected:** We wish that our parents didn’t have to work so hard.
8. **Corrected:** Cultural preservation includes safeguarding intangible heritage like music and dance.
9. **Corrected:** He has been fixing the car in the garage for weeks because it kept breaking down.
10. **Corrected:** Minh and Quang had a picnic in the garden at 3 p.m. last Saturday.
11. **Corrected:** She wishes she had a villa with a swimming pool and a beautiful garden.
12. **Corrected:** We should protect valuable artefacts from being stolen or sold illegally.
13. **Corrected:** I wish I could read minds and know what people are thinking.
14. **Corrected:** The baby was sleeping peacefully when the phone rang loudly.
15. **Corrected:** My sister attended a cooking class to learn how to make new recipes three months ago.

Feel free to ask for any further assistance!