Question

according to the theory proposed by harry hess, what causes continents to move?
continental drift
magnetic polarity
seafloor spreading
deep - ocean trenches

Explanation:

Harry Hess proposed the theory of seafloor spreading. In this theory, new oceanic crust is formed at mid - ocean ridges and then moves away from the ridge. This movement of the oceanic crust (seafloor) can cause the continents (which are on top of the tectonic plates) to move. Continental drift was a prior concept that Hess's work helped to further explain. Magnetic polarity is related to the Earth's magnetic field reversals recorded in rocks but is not the direct cause of continental movement in Hess's theory. Deep - ocean trenches are areas where old oceanic crust is subducted (sinks back into the mantle) but are more about the recycling of oceanic crust rather than the cause of continental movement.

Answer:

seafloor spreading