Task: Question Answering
Input (English): Question: When performing the Ames test, what result would reveal that the compound is a mutagen? 
 Options:  <1> Abnormal division in mouse uterus cells. <2> Abnormal growth in mouse. <3> Proliferation of a hamster ovary cell culture. <4> Reversal in the growth characteristics of Salmonella. <5> No option is correct.
Output (English): 4