[单项选择]

A few milliamps of electricity can cause plants to increase synthesis of chemicals. These compounds often also have a pharmacological (related to medicine) or commercial value, so the trick could be used to help increase yields of commercially useful biologicals. Artemisinic acid, from sweet wormwood, for example, is used in malarial medications, and shikonin (紫草素), from the purple gromwell plant, is used against skin infections.
Researchers have long known that stressing plants can force them to take defensive action, often ramping up the production of protective chemicals that, for example, make them more resistant to insect attack. It has become common practice to stress such plants into increasing their yields. This is usually clone using physical stress elicitors (诱导子), including bits of the micro-organisms that normally attack the plants, or irritants made from metallic compounds such as copper chloride. These are effective, but they come at a cost. Most elicitors a
A. Reactions to the electric stress lead to more chemical yields.
B. Yields of commercially useful biologicals are increased.
C. Using electricity to elicit chemical production is very exciting.
D. Using electricity has a negative effect on plant growth.

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