Question

5．Why does the sky change colors？
What is the sky？How high is it？What color is it？What birds can live above it？These questions are difficult to answer，aren't they？
In fact，the sky has no color．Then why does the sky look blue？
We know that there is air around the world．When planes fly，they need air to lift their wings．Planes can't fly very high．That is because the air gets thinner when they go higher．The same will happen to us if we go high enough．If we go up about 1，200 kilometers from the earth，we'll find no air there．Some birds can fly into the sky as high as a plane，but they cannot fly or live without air．
Looking up above us，you will see the blue sky with white clouds．It is usually light blue．The color would be bluer when you see on the top of a high mountain．And you will see fewer clouds in the sky between you and the sun．
Sometimes the sky doesn't look blue．When the sun rises and falls，you will see red orange，and other colurs in the sky．Such are the most beartiful moments of the day．
Who can see the colors of the sky high above the earth？The astronauts!They can see those beautiful colors of the sky from the outer space．However，before flying into outer space，they sit in a spaceship high above the earth，and there is no air at all．The sky would be that dark and its color would be black．
Now you may understand that we see colors because the air scatters（使散射）the sunlight．Light travels through the air．Without air，there would be no light or colors．

34．Planes can't fly as high as possible becauseD．
A．the sky is blue
B．the wings are heavier
C．the sky has no color
D．the air becomes thinner
35．When you stand on the top of a high mountain，you will seeB．
A．more air
B．bluer skies
C．more colors
D．more clouds
36．In Huzhou，we might see many colors in the sky atAduring the day．
A.6：00a．m．
B.9：00a．m．
C.1：00p．m．
D.3：00p．m．
37．The sky changes colors becauseD．
A．it's colorful itself
B．the world is colorful
C．the air has colors
D．the air scatters the sunlight．

Answer 1

分析 本文主要介绍了天空为什么有变化多端的颜色．

解答 34．D 细节理解题．由第二段中的"Planes can't fly very high．That is because the air gets thinner when they go higher"可知，飞机不能尽可能 高地飞行是因为随着高度增加空气会变得越来越稀薄．故选D．

35．B 细节理解题．由第四段中的"The color will be bluer when you see on the top of a high mountain"可知，当你站在高山顶上，你会看到 更蓝的天空．故选B．

36．A 细节理解题．由第五段中的"When the sun rises or falls，you will see red，orange，and other colors in the sky"可知当太阳升起或落下时，你会看到天空中有许多颜色，故选 A．

37．D 细节理解题．由最后一段中的we see colors because the air scatters （使散射） the sunlight"可知我们看到的颜色是因为空气散射的阳光，故D项符合题意．

点评 做题时要在理解好文意的基础上，与题目有机的结合，从文章中找到相关细节性的句子与选项细细比对，进行选择或推理判断，选出符合文章内容的正确选项．做题注意灵活，有时可采用排除法或直选法确定出最终答案．