question:  What clue proves the natural existence of water on the moon?
context: The meteor, a pebble, a little larger than a match head, traveled through space and time since it came into being. The light from the star that died when the meteor was created fell on Earth before the first lungfish ventured from the sea. In its last instant, the meteor fell on the Moon. The shaft tried to tie itself into a knot, and the blades, damaged and undamaged were spit through the casing. Once he followed a stampede to Yellow Crater, where he thought for a while that he had a fortune in chromium. By the light of this, he reinspected the steam system, and found about three gallons of water frozen in the condenser. When the meteor pierced the turbine, the water in the condenser began to boil. This boiling lowered the temperature, and the condenser demonstrated its efficiency by quickly freezing the water in the tank. Then, if the pump wasn't blocked by ice, it would return the water to the boiler. The water that he had poured into the boiler quickly turned into steam, and the steam turned the generator briefly. This was to allow the air-conditioning system to function properly, and to prevent air loss in case of the highly improbable meteor damage. For example, because of an order of his stating that there would be no alcoholic beverages within the survey building, the entire survey was assured of a constant supply of home-made, but passably good liquor. Morning to him had no meaning at all, but he thought in the strictest sense that it would be morning on the Moon for another week. It was used mostly, from sun-up to sun-down, to supplement the nuclear power plant. Three of the nine banks of mirrors would not respond to the electric controls, and one bank moved so jerkily that it could not be focused, and it threatened to tear several of the mirrors loose. "Meteor shower," Cowalczk answered, "and that's not half of it.
output:  The presence of specific minerals
options:  The ability to distill alcohol  Increase of meteor activity  Humans are able to survive for long periods of time  The presence of specific minerals