陈述句：There is a boy at the door.
疑问句：is there a boy at the door?
回答： Yes,there is / No,there isn't
否定句： There is not a boy at the door.
欢迎追问，望采纳！
There isn't a boy at the door
isn't there a boy at the door? Yes ,there is . No ,there isn't
祝你学习进步
There is not a boy at the door.
Isn't there a boy at the door? Yes ,there is . No ,there isn't
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