This is a book的否定句,一般疑问句,及肯定,否定回答

This isn't a book.
Is this a book?
Yes,it is.
No,it isn't.
请指出,希望能和你一起探讨~
如果认为我的回答好的话,请及时采纳,我想请问，This isn't a book.和This is not a book.哪个对？？？？都对，isn't是is not的简写。