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.
