The correct answer is b, clerical. During the 50's, it was considered unladylike for a woman to be employed unless it was absolutely necessary. Women who worked were typically single and supporting themselves; married women were supposed to stay home and raise children. Those who did work were employed as secretaries, telephone switchboard operators, and other jobs considered appropriate for women. Although women had worked in industry during the war years, it was considered their duty to surrender those jobs to men returning from the war upon its completion. Women in professions, other than nursing, were considered virtually heretical. A trustee of Barnard College once commented:
God protect us from the efficient go-getter businesswoman whose feminine instincts have been completely sterilized.
So the correct answer is that most working women in the 50's were in clerical positions.