十万个为什么·科学阅读30篇（3）
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Why Do Leaves Change Color in Fall?
秋天树叶为什么会变色？
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In spring and summer, leaves are green.春夏时节，树叶是绿色的。
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They contain a green pigment called chlorophyll.叶子里含有一种叫叶绿素的绿色色素。
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Chlorophyll helps plants make food from sunlight.叶绿素帮助植物利用阳光制造养分。
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When days get shorter in fall, trees stop making it.秋季白昼变短，树木便停止合成叶绿素。
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Other colors like yellow and orange were always there.黄色、橙色等其他颜色原本就存在于叶中。
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They just could not be seen before.只是此前被绿色掩盖，无法显现。
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Red color comes from sugar trapped in leaves.红色则来自滞留在叶片中的糖分。
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Then the leaves fall off to save water.随后树叶脱落，以减少水分流失。