How are convection currents produced in the air?

A
Warm air is less dense, so it rises. Cold air moves in to take its place.
B
Big weather events like hurricanes and tornadoes cause convection currents.
C
Cold air is less dense, so it rises. As the cold air rises, warm air descends.
D
Wind causes convection currents by stirring up the air.

A. Warm air is less dense, so it rises. Cold air moves in to take its place.