In the Ames Test, What Happens When His- Bacteria Are

In the Ames test, what happens when his- bacteria are exposed to a chemical and experience a higher level of growth than the control?

A) A reversion mutation allowed the his- bacteria to regain their ability to make histidine (revert to his+) .
B) The his- bacteria now utilized histidine from the media.
C) The reversion rate is lower than seen for spontaneous mutations.
D) The tested chemical is regarded as a non- mutagen.
E) The his- bacteria utilized DNA repair tools to fix the mutation.