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  3. Trees are so common arid quiet that we pay them little mind. What, for instance, should we answer when asked to name the biggest

Trees are so common arid quiet that we pay them little mind. What, for instance, should we answer when asked to name the biggest

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问题     Trees are so common arid quiet that we pay them little mind. What, for instance, should we answer when asked to name the biggest living thing Earth has ever seen? Dinosaurs? Blue whales? No, the largest sequoias in northern California weigh more than six blue whales.  The tallest redwoods and Australian eucalyptus trees tower more than 300 feet high, three times the length of the greatest dinosaur.【71】Some bristlecone pine trees in the American West are more than 4, 000 years old, seedlings at the time the Egyptians were building the Pyramids.   Trees sustain our lives and our planet in a thousand practical ways. This morning at breakfast—in your wood-framed house, on your wooden kitchen table—you might have enjoyed orange juice or a grapefruit. Both come to use from trees. Over your French toast you may have sprinkled cinnamon and nutmeg, the powdered bark and nuts of tropical trees. That quart of maple syrup on your table was boiled down from roughly 10 gallons of sap from a sugar-maple tree.【72】Do you like chocolate, almonds, cola beverages.’? Cocoa beans, almonds and kola nuts are tree products.   Frees do more than mule life pleasant; they make life possible. Trees get water through their roots and, primarily through their leaves, they draw carbon dioxide from the air. Then, with the action of sunlight on cells containing chlorophyll and other materials, chemical reactions occur, and oxygen is released.【73】Photosynthesis also produces glucose, a type of sugar. Trees convert some of the glucose to starch, which they use for energy storage. The cellulose fiber we call wood is made of thousands of glucose molecules linked into giant chains that no longer taste sweet.【74】The ancient Greeks, for example, treated pain with a tea made by boiling willow leaves and bark, a tea modern scientists now know contains silicon, a precursor of acetylsalicylic acid—aspirin.【75】More recently, researchers isolated and synthesized the chemical ginkgolide from the tree for use in treating asthma, toxic shock and other ills.   
A. For centuries, the Chinese have derived medicines from the ginkgo tree.   
B. Through photosynthesis, an acre of trees produces enough oxygen to sustain three humans.   
C. As scientists unlock the secrets of trees, they uncover surprising tacts.   
D. Trees have always been green machines, producing substances that humans learned to use.   
E. You think, at 150 or more years, giant tortoises can live a long time?   
F. And the morning newspaper was printed on the processed wood pulp we call paper.
选项
答案B
解析
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