How ________ you? （   ）

A．am

B．are

C．is

找出错误并改正：What is these?__________

用所给词的正确形式填空。
1. We can use solar panels to__________(change)sunlight into electricity.
2. It __________（be）motion energy.
3. They come from the remains of dead __________ (plants) and __________ (animals).

Everyone ____ to their teacher in the classroom. （ ）

A．are listening

B．is listening

C．listen

用括号里单词的适当形式填空
1. When I am ________ (do) my homework, my mother is ________ (cook).
2. He has to _________ (travel) the country in search of work.
3. How __________ (do) seeds travel?
Seeds _________ (travel) in many ways.
4. What _____ (be) they talking about?
They are _________ (talk) about the seeds of plants.