In View of the Present Surface and Atmospheric Conditions on Mars

In view of the present surface and atmospheric conditions on Mars, why would there be no liquid water on its surface?

A) The water would all be frozen, given the prevailing day and night temperatures.
B) The very low atmospheric pressure would allow the water to boil and evaporate rapidly.
C) Water would have reacted chemically with the surface rocks.
D) The UV radiation from the Sun would have dissociated the water molecules into hydrogen (which would leave the planet) and oxygen (which is still present) .