The answer is D. President Mckinley's desire for war
They joined with the democrats to support with William Jennings Bryan.
I would say “C”. Before that, the United States had never been involved in any international conflict where many nations participated. But after America’s involvement, the war turned in the Allies favor fairly quick.
The two groups were the managers,
who managed the factory, and tool the decisions of what and how will be produced,
and the labourers, who actually participated in the production process ( i.e. were in a production line or similar).