Answer:
using a ruler to scratch the skin under the cast
Explanation:
So its acquired immunity and the cells responsible are the B lymphocytes that produces antibodies against the virus. Memory is keep since first encounter of the virus by the immune system by way of the antibodies that was initially produced. The antibodies are there already, which makes it fast to act upon when expose again.
I think your answer for this question is D . I may be wrong ... but I think it's D
