The diagram shows the movement of magma due to convection currents. An illustration of the inner core, the outer core and the crust of the earth. Between the outer core and the crust is labeled mantle. In the mantle is sets of arrows in the clockwise direction. In the crust are arrows going both right and left from the center. The crust then is curling into the mantle.
Based on the diagram, which part of Earth is the coolest?

the crust
the mantle
the outer core
the inner core