Looking at Your Results of the Ames Test,using Bacteriological Agar

Looking at your results of the Ames test,using bacteriological agar medium plates lacking the amino acid histidine,you find that there are many colonies growing on the agar.Your interpretation of this result is:

A) the bacterium has turned its operon genes on,producing proteins necessary for growth.
B) the chemical being tested is mutagenic.
C) the bacterium does not have any plasmids,so it cannot grow on the medium.
D) the drug being tested has no inhibitory effect on the bacterium,therefore it is not a good antibiotic to give for treatment of disease.