Here are the correct tenses for the sentences provided:

1. We **finished** our dinner half an hour ago.
2. The farmers **worked** in the field now.
3. Mrs. Green always **goes** to work by bus.
4. My parents **have lived** in London. They **have been** there for 20 years.
5. She paid for her ticket and **left**.
6. She **sat** under a tree when it **began** to rain.
7. How many times **have you seen** him since he went to Edinburgh?
8. Mr. Davy **has worked** in the same place for thirty years and he is not planning to leave.
9. Rivers usually **flow** to the sea.
10. Do you know that man who **smokes** there?
11. My brother **has worked** in this factory since 2005.
12. I **washed** my hair before breakfast this morning.
13. What was Tom **doing** when you saw him?
14. How often do you **read** a newspaper?
15. He **has played** football since he **was** ten years old.