When 68-year-old Mrs. Blake had a flat tire on a fairly isolated highway, she received help from a passerby in less than 10 minutes. One year later, when she had a flat tire on a busy freeway, an hour elapsed before someone finally stopped to offer assistance. Mrs. Blake's experience best illustratesA. the mere exposure effect.B. altruism.C. the self-fulfilling prophecy.D. the bystander effect.