怎么确定是不是无关选项啊

bunnyfdu2015

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 ______.

一种草生长在土里，土里有金属对其他作物有毒

一些人发现-草产生h使金属变惰性

所以，h使草在富含金属的土壤里生长____

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

就剩DE，我觉得E不是无关选项啊，这题选D