Which finding, if true, would most directly support the researchers' … | Verbal SAT Question

Asia’s Gobi Desert and California’s Central Valley are the main sources of dust in western North America’s Sierra Nevada mountains. To investigate their relative contributions, Sarah Aciego et al. recorded the isotopic signatures of dust collected at a low elevation site (the San Joaquin Experimental Range) and two higher elevation sites (Providence and Soaproot) in the Sierra Nevada, as well as the isotopic signatures of Gobi and Central Valley dust. Aciego et al. concluded that while the contribution of Central Valley dust, which has a lower ratio of strontium-87 to strontium-86 (87Sr/86Sr) than Asian dust does, remained mostly unchanged at the lowest elevation site for the duration of the study, the contribution of Central Valley dust increased at higher elevations.

Which finding, if true, would most directly support the researchers’ conclusion?

Over the course of the study, the 87Sr/86Sr ratio of dust collected at the San Joaquin Experimental Range was relatively constant, whereas the 87Sr/86Sr ratios of dust collected at Providence and Soaproot decreased.

As the study went on, the 87Sr/86Sr ratios of dust collected at Providence and Soaproot grew closer to the 87Sr/86Sr ratio of dust from Asia, whereas the 87Sr/86Sr ratio of dust collected at the San Joaquin Experimental Range grew closer to the 87Sr/86Sr ratio of dust from the Central Valley.

Throughout the study, the 87Sr/86Sr ratio of dust collected at the San Joaquin Experimental Range was consistently higher than the 87Sr/86Sr ratios of dust collected at Providence and Soaproot.

The 87Sr/86Sr ratios of dust collected at all three sites were closer to the 87Sr/86Sr ratio of Asian dust than to the 87Sr/86Sr ratio of Central Valley dust.