The correct answer is d. They went to work in war-related industries to fill in for the men who were away at war.
During World War II, millions of men were drafted to serve in the United States military. This left millions of jobs open on the homefront. The result was a significant increase in the amount of women working in war-related industries.
The enormous need for guns, ammunition, tanks, etc. resulted in women all over the country breaking traditional gender roles by working in war-related industries. This movement was spurred by propganda, with one of the most famous ones being the Rosie the Riveter campaign.