xdf q178

he_cathy

Which of the following most logically completes the argument?

A certain cultivated heab 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 histidince 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.

不明白答案为什么是E？？请高人指点！！

he_cathy

怎么都每人搭理我？

crazyep

我觉得答案应该是 C。呵呵

闲云漫舞

A certain cultivated heab 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_____,

XDF补充材料上178不是这题，不知楼主哪儿来的。

开始我选D，但觉得没有提到关键词histidine，如果改成因为这种化学物质使它适合生长我觉得是对的。

E我是这么解释的：
题目要求　植物有某化学特性－＞此植物能生长在特殊地方的假设成立
加强结论。

分析：由于这种植物有特定化学特性，所以在mental-rich的地方就能使mental inert；当这些mental intert后，植物就不需要produce那么多histidine，所以开始减少；而这正是植物生长的条件。建立桥梁。

不知这么解释是否正确，欢迎指正。

he_cathy

楼上说的也有道理，可是，文章并没有指出土地什么时候会mental inert，如果选E，还需要假设该植物nature的时候，土地就inert

he_cathy

接着上帖。 我是选C，因为文章开头有提到该植物是one of a group of closely related plants。

PS：这是XDF暑假出的最新版

闲云漫舞

同意楼上，觉得C更直接。BTW：XDF出东西好快，我落伍了。

kingsoft

     i vote for  C

winsx2008

同意c  e中的marturity原文中并没有信息