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 Guimarã, and Pedro Sérgio Fadini did not find this correlation in a study conducted in Brazil, leading some scientists to hypothesize that the pattern is particular to North America. However, Kerstin Leopold, Anja Zierhut, and Jessica Huber reported dissolved organic carbon and mercury rising or falling together in a study conducted in Germany, and several other studies from outside North America have yielded similar results, suggesting that ______

bodies of fresh water outside North America are more likely to show a negative association between dissolved organic carbon and mercury levels than a positive association.

there may be circumstances specific to the bodies of water examined in Fagnani, Guimarã, and Fadini's study that disrupted a general positive association between dissolved organic carbon and mercury levels.

environmental characteristics unique to Brazil likely result in dissolved organic carbon and mercury levels in bodies of fresh water both being significantly higher there than elsewhere.

the bodies of water examined in Fagnani, Guimarã, and Fadini's study may be more similar to the bodies of water examined in studies conducted in North America than to those examined in Leopold, Zierhut, and Huber's study.