Here are the suitable words and verb forms filled in for the blanks:

**Question 5:**
1. They **are doing** their best to learn French.
2. I'll **fix** the parcel first.
3. Could you **do** me a favour, please?
4. Please **turn** off the lights before you go to bed.
5. They can't **fix** my washing machine.
6. I'm going to **do** mathematics at school tomorrow.

**Question 6:**
1. The letter I **received** yesterday is on the desk.
2. This film is the best one I **have ever seen**.
3. She always **remembers** the names of the people that she meets.
4. What are you **doing** now? - I **am learning** English.
5. I **haven't seen** him since he **left** this school.
6. I usually read the newspaper while I **wait** for the bus.
7. The sky is very dark. I think it **is going to rain**.
8. I **haven't invited** Richard yet.
9. Five minutes after we **arrived** at the beach, it **started** to rain.
10. We should go home. It **is getting** darker and darker.
11. Before I **go** to live in Spain, I **thought** it was a hot country.
12. I **tried** to get hold of you for 10 minutes.

Feel free to ask if you need anything else!