question:  How often does the Lunar colony get supplies delivered from earth?
context: Once in two weeks Earth-time a rocketship came around the horizon from Lunar City with stores for the colony deep underground. Come nightfall Pop lowered the supplies down the long cable into the Big Crack to the colony far down inside, and freshened up the landing field marks with magnesium marking-powder if a rocket-blast had blurred them. There is nothing like it on Earth, of course. When it was first found, scientists descended into it to examine the exposed rock-strata and learn the history of the Moon before its craters were made. There were air-tight bulkheads for safety, and a hydroponic garden to keep the air fresh, and all sorts of things to make life possible for men under if not on the Moon. In the Moon's slight gravity, a man is really adjusted to existence when he has a well-developed case of agoraphobia. All of which happened back on Earth and a long time ago. He usually reached the moondozer about the time the ship began to brake for landing, and he watched it come in. The pilot killed all forward motion just above the field and came steadily and smoothly down to land between the silvery triangles that marked the landing place. In each two Earth-weeks of working, the mine-colony nearly filled up a three-gallon cannister with greasy-seeming white crystals shaped like two pyramids base to base. The sun rose very, very slowly in what by convention was called the east. It took nearly two hours to urge its disk above the horizon, and it burned terribly in emptiness for fourteen times twenty-four hours before sunset. At the same time, liquid air from another tank evaporated to maintain the proper air pressure in the shack. Then the apparatus reversed itself and supplied fresh air from the now-enriched fluid, while the depleted other tank began to fill up with cold-purified liquid air. The occupation made it absurdly easy to live on the surface of the far side of the Moon, whether anybody else could do it or not.
output:  Every two weeks
options:  Every twelve days  Every three months  Once a month  Every two weeks