根据短文内容用方框内所给单词的正确形式填空，每空一词，每词一次。

    If you are asked the question "What colour is the sky?" I believe you will answer blue. But I am afraid you are. The sky has no color. When we see blue, we are looking  the blue sunlight. The sunlight  on the little bits of dust(灰尘) in the air.

    Is the sky full of ? I am sure that you are asked this question, . We know that there is air all around the world. We could not live air. Planes could not  if there is not any air. If we go far enough  from the earth, then we will find there is no air. Perhaps we can answer some of our questions now. is the sky? The sky is space. It is all around the world. There is nothing but the sun, the moon and the stars space.