Which of these conditions would likely cause the tectonic plates of earth to stop moving? a) earth’s crust and mantle reach thermal equilibrium. b) earth stops receiving energy from the sun c) the temperature of the surface of earth drops considerably. d) the amount of radiogenic heat released by the mantle multiplies.

Correct
"a) Earth’s crust and mantle reach thermal equilibrium."

The tectonic plates movement is due to the heat convection that happens in the Earth. By the Earth reaching a thermal equilibrium, that tectonic plate movement would stop. We can take for example the big Atlantic ridge. If the big Atlantic ridge were to stop emanating lava from the interior because the Earth had reached a thermal equilibrium, the plates that are moved because of the ocean floor spreading resultant from this mentioned ridge would stagnate.

The second one is the answer edg.