help with convection?

Question

this is the question

convection takes place because
A.warmer air is more dence than light air
B.warmer and cold air have the same density
C.cold air is less dence than warm air
D.cold air is more dence than warm air

It is not A but please help me out !!!!!!!!!

Answer 1

[edit] Atmospheric convection
In the case of Earth's atmosphere, solar radiation heats the Earth's surface, and this heat is then transferred to the air by convection. When a layer of air receives enough heat from the Earth's surface, it expands, becomes less dense and is pushed upward by buoyancy. Colder, heavier air sinks under it and is then warmed, expands, and rises. The warm rising air cools as it reaches the higher, cooler regions of the atmosphere and becomes denser. Since it cannot sink through the rising air beneath it, it moves laterally and then begins to sink. When it reaches the surface again it is heated, and is drawn back into the original rising column.
So the answer is D

Answer 2

D