A: What kind of book are you reading, Crystal?

B: It's about aliens.

A: Really? There's no such thing as aliens. You know that, right?

B: No, I don't know. I mean, I don't {#blank#}1{#/blank#}those stories about aliens on Earth, but there could be {#blank#}2{#/blank#} on other planets. There must be {#blank#}3{#/blank#} of other planets in the universe.

A: But those planets may be very far away.

B: Well, one day we will be able to {#blank#}4{#/blank#} a very fast spaceship, and we will be able to go there. Or perhaps the aliens can travel huge distance very {#blank#}5{#/blank#}.

A: Maybe. Can I look at the book when you've finished?

    In the {#blank#}1{#/blank#}the moon is not as big as the earth—the {#blank#}2{#/blank#} we live on. And they are far away from each other in the Galaxy. In the Galaxy there is a large {#blank#}3{#/blank#} of stars and planets.

    In 1969, three American astronauts {#blank#}4{#/blank#} the moon in a spaceship, but {#blank#}5{#/blank#} of them {#blank#}6{#/blank#}any living things there. It is very hot in the day and very cold at night. And there is no air there. The {#blank#}7{#/blank#} on the moon is {#blank#}8{#/blank#} for anything to live on. Maybe Mars can have life in the future, but we're not sure {#blank#}9{#/blank#}.

    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 {#blank#}10{#/blank#}.