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 ______.
同意D. 因为" it produces large amounts of histidine, an amino acid that, in test-tube solutions, renders these metals chemically inert.", 所以土壤适合其他植物生长. 而C为无关, 即使成立, 还需要进一步论证是否能不能renders these metals chemically inert.