Просто добавить от себя отрицание.

1) Oh, no. The girls aren't talkning. They are sleeping.

2) No, you are wrong. The mom is cooking dinner.

3) It isn't true. The boy is drawing.  

4)Really, the grandmother is knitting.

5) As you know, the grandfather is reading a newspapper.

6) Look! The cat is running after mouse!

7)The dog is swimming, it is crazy, yes.