178。 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 chemicalty 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 acid

C. others of the closely related group of plants are also found to produce histidine in large quatities

D. cultivation of herb in soil with high concentrations of the metals will, over an extended period , make the soil suitable for plants to which the metal are toxic.

E. the concerntration of histidine in the growing herb decline as the plant approaches maturity

答案E

我认为绿色得部分就是要求获得支持得hypothesis，我自己选了A， A实际上是对原题得一个重复，不是特别好得支持。 但是，E是支持得道理我没有想明白

I think the answer should be C

C. others of the closely related group of plants are also found to produce histidine in large quatities

From it we can conclude that it is the histidine that is protecting all the different kinds of plants grow.

thanks !!!!!!!!!!!!!