[求助]gwd28-28

assurance

28-28: Which of the following most logically completes the argument?

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

为什么选 E呢 我选D

谢谢回复

himba

这是我自己的解释：

题干：一种耕种草本植物属于那种生长于含高量金属的土壤中，这种土质对大多数植物来说是含毒性的。农学家对这种草本植物的研究发现这种植物产生大量的H（一种酸，这种酸在试管里可将金属变成化学性失效）。因此，这种植物产生高H可能就是它可以在含高金属的土壤中生长的原因。这个猜想可能被证实只要。。。。。。

（推理过程：因为其产生大量的H，所以H是它可以生存的原因。其gap在于这个H是可以生存的原因还是特定生存造成的现象。）

选项分析：

A: histidine is found in all parts of the plant – roots, stem, leaves, and flowers H可以这种植物的全身找到。这并不能说明H就是植物可以在高铁土壤里生存的原因，

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 H高，其它酸低，也是一个现象，不能说明H就是原因。

C: others of the closely related group of plants are also found to produce histidine in large quantities 其它相近的植物也高产H，同样，不能说明H是原因。

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 曾经含高铁的土地在栽了这种植物后会变得可以栽其它植物。第一，题干告诉我们含铁的土壤对大多数植物是有害的，也就是说其它植物是不可能在高含铁的土地上存活。但现在可以了，也就是说含铁量下降了。第二，题干中告诉我们在试管里面H可以让铁失效；结合这两点，明显就是H的作用让土中的铁变得不产生作用了。正确。

E: the concentration of histidine in the growing herb declines as the plant approaches maturity 在植物长成后H变少了，不能说明H在植物生长过程中的作用。