Question

in the diagram of the earth's interior, which part drives movements of the plates

Answer 1

Convection currents in the mantle move Earth's tectonic plates. :)

Answer 2

convection of the mantle drives both "ridge push" and "slab pull".

Ridge Push is where new ocean crust is created at a mid-ocean ridge and it begins pushing older material away from the ridge...

Slab Pull is where gravity assists the oldest part of an oceanic plate to get pulled down into a subduction zone, where the crust gets destroyed and eventually recycled.

Hope that helps :o)