sb be +动词ing.肯定句
Jack is listening to the radio.
sb be not +动词ing 否定句
Jack isn;t listening to the radio.
Be sb +动词ing Yes,sb be / No,sb ben't 问句及回答
Is jack listening to the radio?Yes,he is./ No,he isn't
What be sb doing?对动作提问 What is Jack doing?
Who be +.对人提问 Who is listening to the radio?