A、Because there are no plants. B、Because there are no human beings. C、Because there is no air. D、Because there are no animals. C

We have just climbed out of a spaceship onto the surface of the moon. Behind us is the ship, half in the sunlight and half in deep shadow. A few miles ahead is a wall of mountains towering against the black sky. And there, as though resting on the mountains, is a great ball of light, beautifully colored in blue and green and brown with a patch of dazzling white at the top. It is our faraway world —the earth.
    We take a step and rise like prize jumpers —up, float, and down again. Hopping carefully, we explore the valleys, the sloping crater walls, the shadowy crater floors.
    Not a sound can be heard —there is no air to carry sound, no wind; there are no smells, no plants, no animals. There is nothing but rock and dust, blinding sunlight and cold black shadows.