Here are the words or phrases that need correcting:

21. **A** - "Should I be out when you call, just leave a message with my assistant?" (Correct form would be "Should I be out when you call, you should just leave a message...")

22. **A** - "If I have **many homework** to do..." (It should be "much homework" since "homework" is uncountable.)

23. **D** - "my father was reading the newspaper and my **mother watched TV**." (It should be "and my mother was watching TV.")

24. **B** - "Most of their farm work **used to do** by hand." (It should be "was done" instead of "used to do.")

25. **C** - "Mother's Day is celebrated **on second** Sunday in May." (It should be "on the second Sunday...")

So the answers are:
21. A
22. A
23. D
24. B
25. C