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?
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