Which of the following, if true, would most seriously weaken the researcher's conclusion? A. The incidence of brain abnormalities in the general population is as high as that in the group examined. B. The brain abnormalities discovered in those studied are of two distinct kinds. C. A wide variety of violent actions were exhibited by those studied. D. Those studied in the experiment acted violently toward strangers as well as toward people they knew. E. The study drew its subjects from a large geographical area.