15. A consumer magazine surveyed people who had sought a psychologist’s help with a personal problem. Of those responding who had received treatment for 6 months or less, 20 percent claimed that treatment “made things a lot better.” Of those responding who had received longertreatment, 36 percent claimed that treatment “made things a lot better.” Therefore, psychological treatment lasting more than 6 months is more effective than shorter-term treatment. Which one of the following, if true, most seriously weakens the argument?

Вариант ответа 1 - (A) Of the respondents who had received treatment for longer than 6 months, 10 percent said that treatment made things worse.

Вариант ответа 2 - (B) Patients who had received treatment for longer than 6 months were more likely to respond to the survey than were those who had received treatment for a shorter time.

Вариант ответа 3 - (C) Patients who feel they are doing well in treatment tend to remain in treatment, while those who are doing poorly tend to quit earlier.

Вариант ответа 4 - (D) Patients who were dissatisfied with their treatment were more likely to feel a need to express their feelings about it and thus to return the survey.

Вариант ответа 5 - (E) Many psychologists encourage their patients to receive treatment for longer than 6 months.