You conduct an Ames test on a chemical. Following incubation, you see just a few colonies on the control plate, and many, many colonies on the experimental plate to which the chemical was added. What does this tell you about the chemical?
a. The chemical is a food source that can be used by the auxotroph
b. The control plate was toxic to the auxotroph
c. The auxotroph prefers growing in the presence of the chemical instead of on the control plate
d. The chemical is a mutagen, and hence, a likely carcinogen