When a warm air mass and a cool air mass meet, the air mass visually moves upward.

a.) warm
b.) cool

Warm air moves up because its density is lower when the heat excites the air molecules.
A.) Warm

The answer for this question is warm air.

Cell division is important to single celled organisms because it allows the cells to reproduce. through cell division, cells make exact copies of themselves. when single celled organisms go through cell division, they make exact copies of themselves which is how they reproduce.