Answer:
3. Would you like a sandwich? "No thanks, I have just had lunch.
4. Shall I pay the waiter? "No, I have already paid him."
5. We have known each other for ten years.
6. Rayan hasn't texted me since Sunday morning.
7. ...you ate breakfast.
8. The train...arrived.
Explanation:
For the rest it is mainly just the past tense of the word.
For example:
He (eat) breakfast.
He ate breakfast.
