按要求改写下列句子。

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.