For Several Decades Now, Amphibian Species Worldwide Have Been in Decline

For several decades now, amphibian species worldwide have been in decline. A significant proportion of the decline seems to be due to the spread of the chytrid fungus, Batrachochytrium dendrobatidis (Bd) . Chytrid sporangia reside within the epidermal cells of infected animals, animals that consequently show areas of sloughed skin. They can also be lethargic, which is expressed through failure to hide and failure to flee. The infection cycle typically takes four to five days, at the end of which zoospores are released from sporangia into the environment. In some amphibian species, mortality rates approach 100%; other species seem able to survive the infection. However, when adult amphibian skin harbours populations of the bacterium Janthinobacterium lividum (Jl) , chytrid infection seems to be inhibited.
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) A toxin secreted by Jl cells kills Bd cells when both are present together on frog skin.
B) Jl cells infect and kill Bd cells when both are present together on frog skin.
C) Jl outcompetes Bd when both are present together on a frog's skin.
D) The presence of Jl on frog skin causes a skin reaction that prevents attachment by Bd cells.

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