The more probable answer would be B. warm air gradually rises above cooler air.
Drizzles are like the little brothers and sisters of rain. They are the same but the difference would be the sizes of these droplets and their amount. These drizzles are associated with fronts and air masses. When warm air masses and cold air masses meet, they usually make a front, which is the boundary between both. The warm air mass would rise up and the cold air moves under it. The cold air gets trapped in some occasions and these result to drizzles.
