Psychologist: In a study, researchers gave 100 volunteers a psychological questionnaire designed to measure their self-esteem. The researchers then asked each volunteer to rate the strength of his or her own social skills. The volunteers with the highest levels of self-esteem consistently rated themselves as having much better social skills than did the volunteers with moderate levels. This suggests that attaining an exceptionally high level of self-esteem greatly improves one's social skills.
The psychologist's argument is most vulnerable to criticism on which of the following grounds?
【选项】It fails to adequately address the possibility that many of the volunteers may not have understood what the psychological questionnaire was designed to measure.