The correct option is
B Varicella virus
Chickenpox, also known as varicella is a highly contagious disease caused by the initial infection with varicella zoster virus (VZV). The disease results in a characteristic skin rash that forms small, itchy blisters, which eventually scab over. It usually starts on the chest, back, and face then spreads to the rest of the body. Other symptoms may include fever, tiredness, and headache.
So, the correct answer is 'Varicella virus'.