What type of air does cold, dense air often converge with to form a thunderstorm

The type of air would be The cooler and denser air wedges under the less-dense warmer air,
When this air is lifted through the motion upward, it would cause the pressure on the cold front to be reduced. When there is enough moisture mixed within it, it will create Formation of Thunderstorms.

3.1439 im dont think its right but im pretty sure it is

The answer i think is d