Interviewer: You have shown that biofeedback, dietary changes, and adoption of proper sleep habits all succeed in curing insomnia. You go so far as to claim that, with rigorous adherence to the proper treatment, any case of insomnia is curable. Yet in fact some patients suffering from insomnia do not respond to treatment. Therapist: If patients do not respond to treatment, this just shows that they are not rigorous in adhering to their treatment. The therapist's reply to the interviewer is most vulnerable to which one of the following criticisms? ['It does not provide statistical evidence to back up its claim.', 'It precludes the possibility of disconfirming evidence.', 'It overlooks the possibility that some cases of insomnia might improve without any treatment.', 'It depends on the ambiguous use of the term "treatment. "']