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 comes 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.
The organization of the passage can be best described as_________.
选项 A、the comparison between two different roots
B、some examples given to further prove the hypothesis
C、the conclusion of findings
D、an explanation of the findings of an experiment
答案D
解析 第二段第一句为本文的主旨。植物生理学家研究种植在实验瓶中的根，以及在此基础上研究根、芽在植物整体中的关系。本文对这一研究发现做了较详尽的解释。所以选项D为答案。
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