Which One of the Following Contributes to the Utility of the Strains

Multiple Choice

Which one of the following contributes to the utility of the strains of Salmonella typhimurium used in the Ames reversion assay?

A) They are highly permeable to test substances.
B) They are defective in DNA repair and,therefore,cannot readily repair damage done by the test substances.
C) It is very straightforward to assay the conversion of their histidine auxotrophy mutations to histidine prototrophy.
D) all of the choices