Final answer:
The nurse should inform the parent that the vaccine cannot cause polio as it contains killed virus particles.
Step-by-step explanation:
The best response from the nurse would be option A) "The vaccine cannot cause polio because it contains killed virus particles."
Polio vaccines, such as the one being administered to the child, use
killed virus particles
to stimulate an immune response. By using killed viruses, the vaccine cannot cause polio. It is important for the nurse to reassure the parent that the vaccine is safe and will not give the child polio.