Final answer:
The primary purpose of the World War I propaganda poster was to encourage Americans to loan money to the government to help finance the war effort.
Step-by-step explanation:
The primary purpose of the World War I propaganda poster in question b was to encourage Americans to loan money to the government to help finance the war effort. The poster depicted the war as a moral struggle and urged Americans to purchase war bonds. These bonds paid interest and were used to finance a large percentage of the war effort.