Which choice most logically completes the text?

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In a 2014 study that took place in Laos, Stéphane Guédron, Delphine Tisserand, and colleagues found a negative association between levels of dissolved organic carbon and mercury in bodies of fresh water. It may seem reasonable to be skeptical of this finding, since most other studies, such as research conducted in 2015 in Canada by Stéphanie Hamelin and colleagues, have found that dissolved organic carbon and mercury levels rise together. Like the latter study, however, most studies of the topic have been conducted in North America, and many of those study sites have similar characteristics to one another, suggesting that

few of the studies conducted in North America have been able to measure dissolved organic carbon and mercury levels with the same level of precision as in Guédron, Tisserand, and colleagues' study.

the mercury levels reported in Guédron, Tisserand, and colleagues' study were much higher than those reported in the study by Hamelin and colleagues even though the dissolved organic carbon levels reported in the two studies were approximately the same.

Guédron, Tisserand, and colleagues' study may have inadvertently measured a different characteristic of bodies of fresh water than their levels of dissolved organic carbon and mercury.

Guédron, Tisserand, and colleagues' finding may differ from the findings of other studies due to a difference in environmental circumstances that affects the relationship between dissolved organic carbon and mercury in fresh water.