Wind formation is primarily caused by temperature differences in the atmosphere, which leads to differences in air pressure. As warm air rises, cooler air moves in to replace it, creating wind. Other factors, such as the Earth's rotation (Coriolis effect), the constant density of air, and the turning of circulating air currents, also play a role in wind patterns, but the fundamental cause is the temperature differences that lead to pressure changes.
So, the best answer among the options is the temperature differences in the hemispheres.