求救~~GWD 28-28 爭議很久...

GWD 28-28 爭議很久的一題，到底正確答案是?

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 ______.

1. histidine is found in all parts of the plant—roots, stem, leaves, and flowers
           
2. the herb’s high level of histidine production is found to be associated with an unusually low level of production of other amino acids
           
3. others of the closely related group of plants are also found to produce histidine in large quantities
           
4. 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
           
5. the concentration of histidine in the growing herb declines as the plant approaches maturity

1. histidine is found in all parts of the plant—roots, stem, leaves, and flowers
2. the herb’s high level of histidine production is found to be associated with an unusually low level of production of other amino acids无关
3. others of the closely related group of plants are also found to produce histidine in large quantities无关
4. 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
5. the concentration of histidine in the growing herb declines as the plant approaches maturity
                   削弱

i chose D

D

C

D说长期的种植herb，这个土地对其他对金属显示毒性的植物也能成活。

这点文章已经说明了，herb可以在这样的土地里成活，说明herb能降低金属的惰性。但是D说的是herb的结果而并非herb为何会产生这样的结果，即使证明了herb能使得土地里金属减少，也不能说明是什么造成的。C更好，有很多的其他类似的植物在这样的土地里成活也是大量分泌histidine，这样“类似的植物在类似的土地里分泌同一种大量的东西并成活”