Answer:
A. the uneven heating of the Earth
Explanation: Convection currents are created by the uneven heating of the Earth.
Because the Earth is tilted on its axis, some areas receive more solar radiation than others. These areas become warmer, and warmed fluids (air and water) rise and expand outward toward the poles.
Heat is transferred from the warmed fluids to cooler fluids. As a result, the cooler fluids become warmer and rise, and the warmer fluids cool and sink. The circular flow pattern that results is called a convection current.