Question

plate tectonics: divergent boundaries
what is the driving force behind the movement of tectonic plates at divergent boundaries?
gravitational forces
magnetic fields
magma welling from below

Explanation:

At divergent boundaries, magma rises from the mantle below, pushing the tectonic plates apart. Gravitational forces and magnetic fields are not the main driving - forces for plate movement at these boundaries.

Answer:

magma welling from below