学进去

读一读，猜一猜。
1. I am a big circle. My face is red. I think I am your favourite fruit. Guess! What am I?
You are an ___ ___ ___ ___ ___.
2. When I am black, I am clean（干净）. When I am dirty（脏的）, I am white. Everyday we meet in your classroom. And I can tell you many things you do not know before. What am I?
You are ___ ___ ___ ___ ___ ___ ___ ___ ___ ___.
3. It is round and bright. In the day it hangs in the sky and gives out light. But nobody can see it at night. What is it?
It is the ___ ___ ___.