As warm air rises from the equator region, the correct answer is B. it creates a low-pressure system.
Warm air is less dense than cooler air, so as it rises, it creates a low-pressure area beneath it. Additionally, the rising warm air expands and cools as it ascends into the atmosphere, but it does not contract or grow denser (A), nor does its temperature increase (C) as it rises; instead, it typically decreases with altitude. Therefore, the most accurate choice in this context is B.