(A)

   What is the sky? Where is it? How high is it? What lies above it? These questions are difficult to answer, aren't they?

   Is the sky blue? The sky has no colour. We know that there is air around the world. When planes fly, they need air to lift their wings. Planes cannot fly  very high because when they go higher, the air gets thinner. If we go up about  1,200 kilometres from the earth, we find there is no air.

   Perhaps we can answer some of our questions now. The sky is space. In  this space there is only the sun, the moon and all the stars.

   1. What is the sky?     .

   A. It's the clouds          B. It's space

   C. It's air             D. It's nothing

   2. The sky     .

   A. is blue              B. is white

   C. is black             D. has no colour

   3. Planes cannot fly very high because     .

   A. the air becomes thinner

   B. the flying machine is not good

   C. people will be afraid if the planes fly too high

   D. it is not necessary for planes to fly so high

   4. If we go up about 1,200 kilometres from the earth, we find    .

   A. there is more air         B. there is less air

   C. there is nothing but air      D. there is no air

   5. In space there is     .

   A. nothing

   B. air everywhere

   C. everything

   D. only the sun, the moon and all the stars

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