Only recently have investigators considered using these plants to clean up soil and waste

Only recently have investigators considered using these plants to clean up soil and waste sites that have been contaminated by toxic levels of heavy metals—an environmentally friendly approach known as phytoremediation. This scenario begins with the planting of hyperaccumulating species in the target area, such as an abandoned mine or an irrigation pond contaminated by runoff. Toxic minerals would first be absorbed by roots but later relocated to the stem and leaves. A harvest of the shoots would remove the toxic compounds off site to be burned or composted to recover the metal for industrial uses. After several years of cultivation and harvest, the site would be restored at a cost much lower than the price of excavation and reburial, the standard practice for remediation of contaminated soils. For example, in field trials, the plant alpine pennycress removed zinc and cadmium from soils near a zinc smelter, and Indian mustard, native to Pakistan and India, has been effective in reducing levels of selenium salts by 50 percent in contaminated soils.

Which of the sentences below best expresses the essential information in the highlighted sentence in paragraph 6？ Incorrect choices change the meaning in important ways or leave out essential information.

A．Before considering phytoremediation, hyperaccumulating species of plants local to the target area must be identified.

B．The investigation begins with an evaluation of toxic sites in the target area to determine the extent of contamination.

C．The first step in phytoremediation is the planting of hyperaccumulating plants in the area to be cleaned up.

D．Mines and irrigation ponds can be kept from becoming contaminated by planting hyperaccumulating species in targeted areas.

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