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阅读理解
Yellow，orange，red and green梩ree leaves make autumn a colourful time!Who paints all these colours?It is the leaves themselves.Inside a leaf，there are millions of little colour
'bags'.They ale green，yellow and orange.The green ones are called chlorophyll (叶绿素).The yellow ones are called xanthophylls(叶黄素).The orange ones are carotene(胡萝卜素).
In the summer，the green chlorophyll is very，very busy.It makes food for the tree.It catches sunlight to change water and carbon dioxide(二氧化碳) into sugar.This sugar is the food for the tree.It is so busy that it covers up all of the other colours in the leaf.
When the weather grows colder in autumn,there is less light and water for trees.The trees will have a rest and get ready for winter.They've made enough food in summer.The leaves no longer need water to make food.
Without the water,the green chlorophyll starts to go away.The other colours in the leaf梩he yellow xanthophylls and the orange carotene come out.So，the leaves don't really turn a certain colour梩hey just lose their green!
But how about the red，purple and green leaves?The leaves look red or purple because they have some sugar in them.They steal some food from the tree!The green leaves are from the evergreen trees(常青树).The evergreen trees stay green all year long.Their leaves don't lose water in winter. | 
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