Nhận biết (M1)

Many studies have found a positive association between levels of dissolved organic carbon and mercury in bodies of fresh water undisturbed by human activity. Méphane Guédron, Delphine Tisserand, and colleagues did not find this correlation in an examination of freshwater bodies impacted by wastewater, but Michael E. Berndt, Wes Rutelonis, and Charles R. Regan, who studied freshwater bodies disturbed by mining, did find it, leading some scientists to hypothesize that wastewater affects water chemistry differently than mining does. Guédron, Tisserand, and colleagues' study, however, was conducted in Laos, whereas Berndt, Rutelonis, and Regan's study was conducted in the United States, suggesting that __________

Which choice most logically completes the text?

• A.

  levels of dissolved organic carbon and mercury are both much higher in bodies of fresh water impacted by wastewater than they are in bodies of fresh water disturbed by mining.

• B.

  bodies of fresh water impacted by wastewater are more common in Laos than in the United States.

• C.

  the discrepancy in the two studies' results may be attributable to underlying environmental differences rather than the effects of wastewater and mining.

• D.

  disturbances related to wastewater likely affect significantly more bodies of fresh water than disturbances related to mining do.