The correct option that identifies the forces influencing the movement of Earth's plates is D: convection and gravity.
- Convection in the mantle creates currents that help to move the tectonic plates.
- Gravity also plays a role, especially in processes like slab pull, where denser, subducting plates are pulled downward by gravity.
Other options may mention significant factors, but D best captures the primary forces involved in plate tectonics.