Here are the past simple forms of the given verbs:

1. watch - watched
2. clean - cleaned
3. return - returned
4. stop - stopped
5. stay - stayed
6. walk - walked
7. shop - shopped
8. tidy - tidied
9. smile - smiled
10. look - looked
11. cry - cried
12. water - watered
13. drop - dropped
14. call - called
15. stay - stayed
16. study - studied
17. play - played
18. help - helped
19. wash - washed
20. climb - climbed
21. finish - finished
22. close - closed
23. dance - danced
24. carry - carried
25. decide - decided
26. laugh - laughed
27. continue - continued
28. explain - explained
29. live - lived
30. arrive - arrived