Which choice most logically completes the text?

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Many studies have found a positive association between levels of dissolved organic carbon and mercury in bodies of fresh water in North America. But Eneiton Fagnani, José Roberto Guimara, and Pedro Sérgio Fadini did not find this correlation in a study conducted in Brazil, leading some scientists to hypothesize that the association is particular to North America. However, several other studies conducted outside North America, such as one by Rasmus Sørensen and colleagues in Sweden, showed similar results to the North American studies, while few have produced results similar to those of Fagnani, Guimara, and Fadini's study, suggesting that _____

the hypothesis that the positive association is particular to North America is correct.

levels of dissolved organic carbon and mercury in bodies of freshwater are both much higher in Brazil than elsewhere.

dissolved organic carbon and mercury levels do typically rise and fall together in fresh water.

there were circumstances unique to Sørensen and colleagues' study that impeded accurate measurements of mercury levels.