The correct answer is A. the temperature gradient.
The temperature gradient is the difference in temperature between two points. The Earth’s surface is warmer at the equator than at the poles. This temperature difference creates a pressure gradient, with higher pressure at the poles and lower pressure at the equator. The pressure gradient drives the wind, which transports warm air toward the poles and cold air toward the equator.
Option B, the development of waves, is not the main cause of the transport of warm air toward the poles and cold air toward the equator. Waves do play a role in the transport of air, but they are not the primary cause.
Option C, the latitude difference, is not the main cause of the transport of warm air toward the poles and cold air toward the equator. The latitude difference does create a temperature difference, but it is not the primary cause of the transport of air.
Option D, the longitude difference, is not the main cause of the transport of warm air toward the poles and cold air toward the equator. The longitude difference does create a pressure difference, but it is not the primary cause of the transport of air.