Answer:
The correct answer is option (D) "His- strain grows on an his- plate".
Explanation:
The Ames test is a procedure that allows to detect if a given compound can cause mutations on a tested organism by growing strains of bacteria that require histidine (His-) to growth, since they are not able to produce its own histidine. In the Ames test, the bacteria is exposed to a given compound and is grown in a medium with small amount of histidine (his- plate). If the His- strain grows on a his- plate, it means that the bacteria has mutated to synthesize its own histidine and it is considered as a positive result on a the Ames test.
