The image below models how air can move by convection at the Earth's equator.
convection current of air at Earth's equator

Which statement best describes this process?
A.
Differences in gravity at various latitudes causes the rising and sinking of air.
B.
Differences in air density cause the rising and sinking of air.
C.
Convection currents are driven by the orbit of Earth around the Sun.
D.
Convection currents on Earth are driven by the gravitational pull of the Sun.