阅读短文, 根据短文内容, 从方框中选择恰当的单词并用其适当形式填空, 使短文意思完整、通顺。

environment,  planet,  earth,  reach,  discover,  universe,  possible,  group,  yet,  none

    In the the moon is not as big as the earth—the we live on. And they are far away from each other in the Galaxy. In the Galaxy there is a large of stars and planets.

    In 1969, three American astronauts the moon in a spaceship, but of them any living things there. It is very hot in the day and very cold at night. And there is no air there. The on the moon is for anything to live on. Maybe Mars can have life in the future, but we're not sure .

    Everything on the moon is much lighter. Walking on the moon is like jumping and flying. So you can jump much higher on the moon than on the .