A. B, D, and D were personally suspected of being involved in a case. A said that the perpetrator was B. B said that the perpetrator was A. C said that the perpetrator was not me. D said that the perpetrator was among us. If one and only four of them are telling the truth, which of the following is true. ['The perpetrator is A.', 'The perpetrator was B.', 'The perpetrator was C.', 'Conditions in the stem are not sufficient to determine who is the perpetrator.']