Populations of Amphibians, Including Frogs and Toads, Have Been Plagued

Populations of amphibians, including frogs and toads, have been plagued by disease and high rates of deformity. A recent study investigated whether problems among the populations have arisen due to poisons from chemicals associated with agriculture. Biologists from the University of Florida collected local adult cane toads Bufo marinus) from more than 20 different locations. Toads were collected from areas close to agriculture- both large-scale and small-scale farms as well as from suburbs located far from agricultural sites. At collection sites where 50-97% of the adjacent land was farmed, males showed high levels of feminization. Feminized male toads were similar in color to females and had lower levels of testosterone and often had deformed gonads. These changes can lead to sterile males or changes in behavior that prevent mating from occurring. Based on this study, what is the control group?

A) male toads collected from the suburbs
B) male toads collected from areas near large-scale farms
C) male toads collected from small-scale farms
D) male toads collected from all the different sites
E) female toads that were not collected