Final answer:
The movement of the mantle as the plates slide around on its top layer is best described as A) convection currents. Hence, A) is correct.
Step-by-step explanation:
The movement of the mantle as the plates slide around on its top layer is best described as convection currents.
Convection is a process where heat is transferred through the upward flow of warmer material and the slow sinking of cooler material. In the case of the mantle, convection currents are responsible for the movement of tectonic plates. Heat from the interior of the Earth causes the mantle material to rise, creating upward flow and pushing the plates apart. As the material cools, it sinks back down, pulling the plates together.
This continuous cycle of rising and sinking material creates a circular motion, driving the movement of the plates on the Earth's surface.