1.he can come now:
Question:Can he come now?
Question:when can he come?
Negative:He can't come now.
2.there is a newspaper on the desk.
Question:Is there a newspaper on the desk
Question:what is on the desk?
negative:There isn't a newspaper on the desk
3.he wants a new car.
Question:what does he want?
Question:Does he want a new car?
negative:He doesn't want a new car.
Question:what does he want?[跟上面重复了.]
4.he is going to come now.
Question:Is he going to come now?
Question when is he going to come?
negative:He isn't going to come now.
--绝对正确!