2. 外语
  3. About fifty years ago, plant physiologists set out to grow roots by themselves in solutions in laboratory flasks. The scientists

About fifty years ago, plant physiologists set out to grow roots by themselves in solutions in laboratory flasks. The scientists

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问题     About fifty years ago, plant physiologists set out to grow roots by themselves in solutions in laboratory flasks. The scientists found that the nutrition of isolated roots was quite simple. They required sugar and the usual minerals and vitamins. However, they did not require organic nitrogen compounds. These roots got along fine on mineral inorganic nitrogen. Roots are capable of making their own proteins and other organic compounds. These activities by roots require energy, of course. The process of respiration uses sugar to make the high energy compound ATP, which drives the biochemical reactions. Respiration also requires oxygen. Highly active roots require a good deal of oxygen.
    The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants. The leaves of the shoots provide the roots with sugar and vitamins, and the roots provide the shoots with water and minerals. In addition, roots can provide the shoots with organic nitrogen compounds. This conies in handy for the growth of buds in the early spring when leaves are not yet functioning. Once leaves begin photosynthesizing, they produce protein, but only mature leaves can "export" protein to the rest of the plant in the form of amino acids.
It can be inferred from the passage that, in the early spring, the buds of plants______.
选项 A、export protein in the form of amino acids
B、do not require water
C、have begun photosynthesizing
D、obtain organic compounds from the root
答案D
解析 推断题型。见第二段第三、四句：根为芽提供有机氮，这对于芽(蓓蕾)在早春的生长很是必要，因为叶在那时还没有起作用。因此可推断出：在那时，植物的芽是从根处获得有机化合物的；所以选项D为答案。
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