A defendant is on trial for manslaughter after he hit a victim in a bar, causing the victim to fall and hit his head on the marble bar top. The defendant claims that he hit the victim in self-defense after the victim lunged at him with a knife. During the prosecution's case, a witness testifies that she heard the victim's friend shout at the defendant, "You just killed a helpless man!" A defense witness is called to testify that he was there and does not remember hearing the victim's friend say anything.Should the defense witness's testimony be admitted?A No, it is irrelevant to any issue in the case.B Yes, it is proper impeachment of the prosecution's witness.C No, it is improper impeachment of the prosecution's witness because it relates to a collateral matter.D No, it is improper impeachment because it does not positively controvert the prosecution witness's testimony, as the defense witness merely says he does not remember.