A study found that patients referred by their doctors to psychotherapists practicing a new experimental form of therapy made more progress with respect to their problems than those referred to psychotherapists practicing traditional forms of therapy. Therapists practicing the new form of therapy, ttherefore, are more effective than therapists practicing traditional forms. Which one of the following most accurately describes a flaw in the argument? ['It ignores the possibility that the patients referred to therapists practicing the new form of therapy had problems more amenable to treatment than did those referred to therapists practicing traditional forms.', 'It ignores the possibility that therapists practicing the new form of therapy systematically differ from therapists practicing traditional forms of therapy with regard to some personality attribute relevant to effective treatment.', 'It presumes, without providing justification, that the personal rapport between therapist and patient has no influence on the effectiveness of the treatment the patient receives.', 'It ignores the possibility that therapists trained in traditional forms of therapy use the same techniques in treating their patients as therapists trained in the new form of therapy do.']