1.It is a watch.
Is it a watch?
Yes, it is
No, it isn't
It isn't a watch
They are watches
2.Bill's ruler is in the pencil-box.
Is Bill's ruler in the pencil-box?
Yes, it is
No, it isn't
Bill's ruler isn't in the pencil-box.
Bill's rulers are in the pencil-box.
3 I have a baseball.
Do you have a baseball?
Yes, I have
No, I haven't
I don't have a baseball.
We don't have baseballs
4.He has a tennis ball.
Does he have a tennis ball?
Yes, he does
No, he doesn't
He doesn't have a tennis ball
They don't have tennis balls