This is an apple 改为否定句,怎么改?

he looks at you
否定句 he doesn't look at you.
一般疑问句 Does he look at you?
回答 肯定 Yes,he does.
否定 No,he doesn't.
This is an apple
否定句 This is not an apple.
一般疑问句 Is this an apple?
回答 肯定 Yes,this is.
否定 No,this isn't.