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 Enelton 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 Heidi Pyhtilä and colleagues in Finland, showed similar results to the North American studies, while few have produced results similar to those of Fagnani, Guimarā, and Fadini's study, suggesting that

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

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

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

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