Evidence for the Loss of Water from the Atmosphere of Venus

Evidence for the loss of water from the atmosphere of Venus via the action of ultraviolet light comes from the

A) observation of auroras high in the Venusian atmosphere caused by the action of ultraviolet light on water molecules
B) fact that today, water is found only in the upper atmosphere of Venus
C) observation of an ozone layer in the atmosphere which is formed from the breakup of water molecules by ultraviolet radiation
D) observation of an excess of heavy hydrogen (deuterium) atoms in the atmosphere which are less easily able to escape once the water is broken apart