Which of the following is our best explanation for the driving force of plate tectonics

These are regions in the asthenosphere (upper mantle of the earth) where heat from the earths core is causing magma to rise through convective flow (where warm fluids tend to rise and cool fluids tend to sink). When the hot magma rises to the bottom of the earths crust, it cant go any further and starts to flow out to the side. This giant river of flowing magma is then the driving force that moves the large masses of the earths crust called the tectonic plates.-I agree.Convection in the asthenosphere.......