Answer:
B. Infectious agent
Step-by-step explanation:
Chicken Pox, a highly contagious disease that spreads from one person to other through a virus Varicella Zoster Virus. this virus is very infectious and even spreads through close contact. Vaccinated person who is considered immune to chicken pox, has also chance of getting this disease again i.e. a person can get this disease twice too but its not much common.