One Explanation for the Increased Participation of Married Women in the U.S.labor

One explanation for the increased participation of married women in the U.S.labor force is that:

A) fewer women are being trained for household work by the public school system.
B) the rapid growth in the service sector has increased job opportunities for women.
C) the cost of professional day care has increased.
D) couples are having more children.
E) husbands earn more today than they did previously.