2. 外语
  3. Plants need green leaves to make food. A plant needs sunlight and carbon dioxide (二氧化碳) from the air for making food and it also

Plants need green leaves to make food. A plant needs sunlight and carbon dioxide (二氧化碳) from the air for making food and it also

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问题    Plants need green leaves to make food. A plant needs sunlight and carbon dioxide (二氧化碳) from the air for making food and it also needs water and salts from the soil to make food too. There are certain cells (细胞) in the leaves which change carbon dioxide and water into sugar. To do this the cells need energy, which they get from the sunlight.
   Green leaves make food for the whole plant. A red leaf can make food too because under the red coloring of the leaf there are food-making cells. There are no leaves that are completely yellow, for they can’t make food.
   The plant makes sugar for its food. In sunlight green leaves make a lot of sugar. The veins (叶脉) can’t carry all this sugar away, so the leaves change the sugar into starch (淀粉), which is kept and so stored in the leaves. At night, the starch change back to sugar. It is then carried away from the leaves. Some of the sugar is used as food by the plant while the rest is stored as starch. In some plants, food is stored in the roots; in others it is stored in the stem and in leaves, fruits and seeds.
Sugar is made for its food by ______.
选项 A、sunlight
B、veins
C、stem
D、green leaves
答案D
解析 第二段的第一句话说：“Green leaves make food for the whole plant.”第三段说“The plant make sugar for its food.”由此可见，是绿叶制造出sugar作为自己的食物，而stem和veins只是sugar流经和储存的地方。
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