A dead version of a virus is introduced into a person. This activates the person's immune system, which learns how to fight the virus. Years later, the person comes in contact with the virus again and does not get sick because his immune system can easily defeat the virus. What has most likely occurred in this scenario so that the person did not get sick during the second exposure? (A)The person developed a vaccine against the virus.
(B)The person was sick from a virus and developed innate immunity.
(C)The person was vaccinated against the virus.
(D)The person was sick from a virus and developed an immune response.