posted by John .
1. I like taking walks.
2. I like taking a walk.
(Which one is OK? Are both right?)
3. You should obey the school rules.
4. You should keep the school rules.
5. You should follow the school rules.
(Are all the same?)
6. He helped Mother who was sick in bed.
7. He helped to carry their bags when they were sick.
8. He did his friends' homework when she was sick.
9. He helped his handicapped friend to go to school.
(Would you checke the expressions? )
All are correct except #8. It should be: He did his friend's homework when she was sick.
Using apostrophes for possessives is tricky -- even for native English speakers.
The basic rule is that if the noun ends with s, as friends, then you add the apostrophe after the s to make it possessive. However, in your sentence, you meant the "homework of your friend," so the possessive is "friend's."
3,4,5. Obeying and following are better than keeping. Depending on the context, keeping the rules might indicate that you were thinking of getting rid of the rules but decided to keep them.
I hope this helps a little more. Thanks for asking.