[求助]蓝皮XDF 178

chen83250245

A certain cultivated herb is one of a group of closely related plants that thrive in soil with
high concentrations of metals that are toxic to most other plants. Agronomists studying
the herb have discovered that it produces large amounts of histidine, an amino acid that,
in test-tube solutions, renders these metals chemically inert. Possibly, therefore, the
herb’s high histidine production is what allows it to grow in metal-rich soils, a hypothesis
that would gain support if ______.
A. histidine is found in all parts of the plant—roots, stem, leaves, and flowers
B. the herb’s high level of histidine production is found to be associated with an
unusually low level of production of other amino acids
C. others of the closely related group of plants are also found to produce histidine in
large quantities
D. cultivation of the herb in soil with high concentrations of the metals will, over an
extended period, make the soil suitable for plants to which the metals are toxic
E. the concentration of histidine in the growing herb declines as the plant approaches
maturity

答案选E，想不通。植物成熟后histidine就减少怎么能说明它是植物成活的原因呢？我感觉D还好一点，起码说明histidine可以降低金属浓度，从而使植物能够生存。

请高手指教。

rainbowgirl

我的理解是，E说明了植物在生长过程中消耗了histidine, 也就是说histidine起了作用。原文里面并没有提到histidine可以降低浓度，所以D是过分推理了