Here are the corrections to the mistakes in the provided text:

**Task 4: Underline and correct the mistakes.**

1. What does they wear at their school?
→ **What do they wear at their school?**

2. Do he go to the library every week?
→ **Does he go to the library every week?**

3. Windy always watch TV at 9 p.m. before going to bed at 10 p.m.
→ **Windy always watches TV at 9 p.m. before going to bed at 10 p.m.**

4. Sometimes, we goes swimming together with her family.
→ **Sometimes, we go swimming together with her family.**

5. How does Linda carries such a heavy bag?
→ **How does Linda carry such a heavy bag?**

**Task 5: Rewrite the sentences below in the correct form.**

1. They always go to the beach in the summer.
2. She often visits her grandparents on Sundays.
→ **(This one is already correct.)**

3. We usually have breakfast at home.
→ **(This one is already correct.)**

4. He sometimes plays guitar at parties.
5. I often read books before going to bed.
→ **(This one is already correct.)**

**Task 6: Fill in the correct verb forms in the sentences.**

1. I **like** tea.
2. He **plays** football in the afternoon.
3. You **go** to bed at midnight.
4. They **do** the homework on weekends.
5. The bus **arrives** at 8:30 a.m.

**Task 7: Fill in "do, does, am, is, are."**

1. **Is** she in the garden?
2. **Is** the cat under the bed?
3. **Do** you like horses?
4. **Does** she want to go to the gym?
5. **Is** John on the train?
6. **Do** they live in Poland?
7. **Do** you worry about the exam?
8. **Does** it rain much in Scotland?
9. **Are** they at the cinema just now?
10. **Are** you hungry?

Feel free to ask if you need further assistance!