C. liquid water once existed
Fresh gully-like characteristics on Mars firmly propose that liquid had floated on the surface in the past. Here we acknowledge the probability that CO2 vapor-supported streams developed the gullies. However, it is noticed that neither condensed CO2 nor CO2 clathrate hydrate is expected to expand in important quantities in the Martian crust.
In addition, if reduced CO2 were operating under lithostatic pressures, the vulnerability to the atmosphere would provide peculiarities which are related to physical pyroclastic flows, not surface runoff.
