xdf 第178题

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 concentration 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,我选c

我认为e随着成熟,histidine减少,这是weaken,搞不懂为什么要选e,而且也不知道c为什么错,

请NN 指教

如果选B other plants are also produce large istidine, 说明other palnts 和 the certain cultivated herb 没有区别, 那么两者应该都可以在富金属污染的土壤里存活,这于原文结论是相反的, 因为原文说the herb is thrive, 但是 most other plants are toxiced , 所以这个选项才是削弱了原文.

E 选项: the herb 原来 produces large amounts of histidine, 但是 declines as the plant approaches maturity, 说明histidine与金属发生了反应而变少,从而避免了植物中毒,解释了原因, E支持了原文的结论the herb's histidine is what allows it to grow in metal-rich soils