The correct answer is - D) the lower mantle being relatively hotter.
The lower mantle plays a crucial role in the geologic activities that appear on the Earth. This is because the lower mantle has much higher temperatures than the surface, as well as having much bigger pressure, and both of these things contribute to the formation of the convection currents in the mantle.
The convection currents are the ones that bring in the high temperature and pressure towards the surface, so they make a lot of pressure on the crust, and eventually crack it. As they have cracked the crust into multiple peaces, all of those peaces are moving because of the convection currents, thus creating all of the geologic activity in meantime.