1. There is a thing.

You break it to use.

Hint（線索）：a kind of food

2. What is as big as an elephant，but weighs（重） nothing at all？

Hint：You can only see it when theres light.

3. What is white when it is dirty and black when it is clean？

Hint：in the classroom

4. What can you catch but cannot throw？

Hint：ill