The movement of earth's tectonic plates relate to many factors, including density differences in the plates and
a. convection cells in earth's atmosphere.
b. convection currents in earth's mantle.
c. the number of species living on each plate.
d. how closely humans monitor plate movements.

The correct answer is - B. convection currents in Earth's mantle.

The movement of the Earth's tectonic plates is driven by the convection currents. The convection currents appear in the mantle layer, and they are currents made out of molten metals with high temperature and very high pressures.

Those high temperatures and pressures have resulted in cracking the crust on the surface of the Earth, thus creating multiple tectonic plates, some very large, some very small.

The pressure from the convection currents is so high that it actually manages to move the plates in certain direction, making them collide/subduct, slide past one another, or move away from one another, shaping up the physical geography of our planet.