Final answer:
Support for prohibition increased during WWI because grain, needed to make alcohol, was required to feed the soldiers. Anti-alcohol sentiment tied in with the era's social reform goals and anti-German sentiment, leading to the Eighteenth Amendment.
Step-by-step explanation:
During World War I, support for prohibition increased partly because the grain used to make alcohol was needed to feed the soldiers (C), a necessity that was considered patriotic, especially in light of rationing measures. The temperance movement was part of the Progressive era's various social reform initiatives, linking morality and patriotism with the anti-alcohol campaign. The sentiment against alcohol was further bolstered by anti-German sentiment during the war, as the brewing industry was associated with German immigrants, facilitating the ratification of the Eighteenth Amendment that outlawed the manufacture, transport, and sale of intoxicating liquors.