Task: Question Answering
Input (English): Context: Think about the longest elevator ride that you've ever taken. Whether you rose five or 100 floors, it probably took less than a few minutes. Now imagine riding in an elevator higher and higher as it climbs for nearly a day. When you reach the top floor, prepare for views that are really out of this world. You'll be in space! Space elevators might sound like a crazy idea, but they're something scientists have been working on for decades. At the moment, riding in a capsule is the only way ordinary people can get to and from space. But those rides are very expensive---about $ 25 million per person per flight. Now scientists are making efforts to reduce the expense of those rides. Researchers are still figuring out the details about how a space elevator might work. One idea is stretching a very long cable -- more than 37,000 kilometers -- up to space from the earth's equator . Objects in space above the equator orbit (......) the earth at the same speed that our planet turns. A weight on the end of the cable would stretch it tight. An elevator tied to the cable could use _ to climb up and down. The only problem is that besides being long, this cable must also be very strong. Storms, including hurricanes might break it. One way to solve this problem is to stretch the cable from the moon instead of from the earth. Airplanes designed to climb higher than a typical jet might take off from the earth and link up with the cable, which would be held in place by the pull of gravity from the earth. An elevator car waiting there would then take riders the rest of the way to the moon. Fueled by solar power, the elevator could transport people and materials without much expense or effort per ride. 
 Question: What may make the cable stay in place on the moon?
Output (English): the pull of gravity from the earth.