Identify the helping verb, linking verb and subject pronouns in each sentence.
16. The mother cat has curled into a ball.
HV-has
LV-
SPN-
17. Kate's kitten has disappeared.
HV-has
LV-
SPN-
18. It is not with the other kittens.
HV-is
LV-
SPN-It
19. I have looked under Dad's chair.
HV-have
LV-
SPN-I
20. We have seen the kitten's paw prints.
HV-have
LV-
SPN-We
All are correct except # 18. Good job!
The only verb in this sentence is IS. Therefore, IS is a linking verb, not a helping verb.