Answer: Gravity causes the higher plates to push away the lithosphere that is placed in the further parts of the ridge. The third force that causes the tectonic plates to move is the slab pull. This force occurs when the older plates start to sink. As the plates age, they become colder, which makes them denser than the mantle beneath them.
Step-by-step explanation:
the correct answer is SLAB PULL !!!!!!!!!!!!!!!!!!