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