25.

1. Can
2. can, must
3. should
4. shouldn't
5. should

26.

1. be jumping
2. staring
3. to do
4. to close
5. speak

27.

1. Very well, thank you.
2. Yes, I must, because it's polite to do it.
3. Yes, I can.
4. To make people feel better when they're sad.
5. Because it's rude to do it.