Here are the completed sentences with explanations:
1. They **played** football yesterday.
* The verb "play" is regular. In the past simple, regular verbs take the -ed ending. So, "play" becomes "played".
2. Mrs. Black **visited** her parents two days ago.
* The verb "visit" is regular. We add -ed to form the past simple: "visited".
3. Tony **lived** in London when he was a child.
* The verb "live" is regular. It already ends in -e, so we just add -d: "lived".
4. Sarah **liked** ice cream.
* The verb "like" is regular and ends in -e, so we add -d: "liked".
5. Mr. Brown **stopped** work at half past five yesterday.
* The verb "stop" is regular. We need to double the final consonant "p" before adding -ed because it follows a short vowel: "stopped".
6. The children **started** school at eight o'clock last week.
* The verb "start" is regular, so we add -ed to form the past simple: "started".
7. You **walked** to school yesterday morning.
* The verb "walk" is regular, so we add -ed: "walked".
8. My friends **studied** at Oxford University these years.
*The verb “study” is regular. We need to change the “y” to “i” before adding -ed. Hence, the word becomes "studied".