The Polar Caps on Mars Are Now Known to Consist

Multiple Choice

The polar caps on Mars are now known to consist of

A) methane (CH₄) , ammonia (NH₃) , and water (H₂O) ices, whose relative abundances vary with the seasons.
B) a combination of carbon dioxide (CO₂) ice and water (H₂O) ice.
C) only carbon dioxide (CO₂) ice, which is very volatile and melts easily.
D) only water (H₂O) ice, which does not melt easily and survives the summer heat.