Earth Has Buckled Slightly Under the Weight of Its Northern

Earth has buckled slightly under the weight of its northern polar cap. Mars has not similarly deformed in response to its northern polar cap. This suggests that

A) the crust and upper mantle must be thicker than those of Earth.
B) any liquid water under the planet's surface must be very near the surface.
C) any life under the planet's surface must be very near the surface.
D) the poles must be 100 percent carbon dioxide ice rather than the more dense water ice.