A Researcher Took Water in Which a Jl Population Had

A researcher took water in which a Jl population had been thriving, filtered the water to remove all bacterial cells, and then applied the water to the skins of adult amphibians to see if there would subsequently be a reduced infection rate by Bd when frog skins were inoculated with Bd. For which of the following hypotheses is the procedure described a potential test?

A) the hypothesis that a toxin secreted by Jl cells kills Bd cells when both are present together on frog skin
B) the hypothesis that Jl cells infect and kill Bd cells when both are present together on frog skin
C) the hypothesis that Jl outcompetes Bd when both are present together on a frog's skin
D) the hypothesis that the presence of Jl on frog skin causes a skin reaction that prevents attachment by Bd cells