Which of the following, if true, could explain the difference in the percentages mentioned in the passage above? A. It was easier to obtain certification twenty years ago than it is currently. B. The majority of those currently in the profession were hired more than twenty years ago, when virtually everyone in the profession was male. C. The women certified in the last twenty years have tended to choose different specialties within the profession than the men have tended to choose. D. Male and female members of the profession have been paid according to equal pay scales for all of the past twenty years. E. Although women currently hold five percent of the full-time positions in the profession, they hold only two percent of the supervisory positions.