Question

what causes earthquakes?
gravity pulls heavy oceanic crust down at a subduction zone.
rock that has been stressed releases strain energy and moves along a fault.
magma rises between plates at a mid - ocean ridge.
rock that has been deformed remains in the new shape when the stress is removed.

Explanation:

Earthquakes occur when stressed rock releases strain energy and moves along a fault. Magma rising at mid - ocean ridges is related to seafloor spreading (not earthquakes). Rock that remains deformed after stress removal is about rock deformation properties (not earthquake cause). Gravity pulling oceanic crust at subduction zones is about subduction mechanics (not the direct cause of most earthquakes). The key theory for earthquake causation is the release of energy along faults due to stress build - up and release in rocks.

Answer:

Rock that has been stressed releases strain energy and moves along a fault.