Bruce Ames constructed a mutagenicity test which initially missed carcinogens which were noncarcinogenic to the tester strains.Why?

A) Tester strains were more resistant to the mutagenic effects of the carcinogen than eukaryotes
B) Not all carcinogens are mutagens
C) Potential carcinogens needed to be modified in eukaryotes before they were mutagenic
D) Histidine biosynthesis was inhibited by the presence of the carcinogens.
E) All of these