1. I'm not sure what I can buy for my brother. ( 改为同义句)
    I'm not sure_____ _____  _____ for my brother.
2. The young man is so a strong that he can carry the heavy box.  (改为同义句)
    The young man is strong _____  _____ carry the heavy box.
3. I really don't know what I should write to him.  (改为同义句)
    I really don't know_____  _____ _____ to him.
4. What's wrong with it? (改为同义句)
    _____  _____ _____ with it?
5. We should help him to write letters. (改为否定句)
    We _____ _____ him to write letters.