johniswritingaletter变一般疑问句.否定句.肯.否回答

问题描述:

johniswritingaletter变一般疑问句.否定句.肯.否回答

john is writing a letter.
一般疑问句Is John writing a letter?
肯定回答Yes,he is.
否定回答No,he isn't.
否定句
John isn't writing a letter.
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