Answer:
Answer is: variations in temperatures inside Earth forces the plates to move
Step-by-step explanation:
Inside the earth, under the crust, we have like a great melted mineral soup at a very high temperature, which increases with depth. Thereby, the upper part is coolest than the deepest one and this generates a movement among the soup, because the coolest magma become heaviest and goes down and the hottest magma goes up creating a cycle called Convection cells that finally force the plates to move.