Final answer:
The World War II poster's main purpose was to encourage citizens to volunteer to help support the war effort by becoming 'citizen soldiers' and engaging in activities that would aid the nation's ability to effectively fight the war. The correct option is c.
Step-by-step explanation:
The main purpose of the World War II poster is C To encourage citizens to volunteer to help support the war. Propaganda during World War II was a critical tool used by the government to boost morale and to encourage civilians to contribute to the war effort in various ways. This could involve enlisting in the armed forces, working in war industries, buying war bonds, conserving resources, and many other activities that would support the soldiers at the front and strengthen the nation's ability to fight effectively.
Posters like the one mentioned often depicted patriotic themes and emphasized the individual's role in contributing to the victory. The government's approach, as seen through the 'newsreel' mentioned, was to train and motivate people to become "citizen soldiers" through different forms of media.