Which choice most logically completes the text?

Source Texts

Text

Many studies have found a positive association between levels of dissolved organic carbon and mercury in bodies of fresh water in North America. But Stéphane Guédron, Delphine Tisserand, and colleagues did not find this correlation in a study conducted in Laos, 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 Ida Tjerngren and colleagues in Sweden, showed similar results to the North American studies, while few have produced results similar to those of Guédron, Tisserand, and colleagues' study, suggesting that ________

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 Laos than elsewhere.

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

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