Answer: Option A.
Mesocyclone is an important part of tornado storm system.
Step-by-step explanation:
Storm system is formed when a center of low pressure emerge with the system of high pressure around it.
A mesocyclone is an important part of tornado storm pressure. A mesocyclone is a storm scale region of rotation in which air rises and rotate around a vertical axis. Mesocyclone I'd formed when there is a strong change in wind speed and direction with height and this spinning wind form a tube-like roll.