The best answer to illustrate the context of a U.S. poster from the World War I era would be:
D. life was changing for women in the United States.
During World War I, many women took on roles that were traditionally held by men as they went off to war, which represented a significant shift in societal expectations and roles for women. This period marked a pivotal moment in the women's rights movement and laid the groundwork for further changes in the decades to follow.