A researcher studying corporate executives found that they tend to have "take charge" personalities, with the predominant traits of assertiveness, decisiveness, and self-confidence. The researcher concluded that people who are more "take charge" than the average person are more likely to become corporate executives. Which of the following, if true, most seriously weakens the researcher's conclusion? ['Many people who aspire to become executives exhibit different management styles in their current jobs.', 'The executives that the researcher studied were often unsuccessful when they tried to manage their family activities as they do their business activities.', 'Holding the job of a corporate executive causes people to develop "take charge" personality traits.', 'Some people who are not executives have stronger "take charge" personalities than some people who currently serve as corporate executives.']