The correct answer is D: the end of the Great Depression.
During wartime, economic stability is crucial to keep the rythm of the troops, their supplies and their movement. There is a need to maintain the factories and the supply of weapons, clothing and food for the army. In order to do this you need money to keep the factories running and the workers happy and coming, and for this you also need to take in account the full employment of these factories and the rest of the country to keep the movement of consumism. This will keep the money flowing into the factories in the first place. When there is scarcity, the government must be intelligent enough to manage moments like this, specially making use of the scarce resources: when to import, when to export, when is the time to ask for a loan, when is not, etc.
The end of the Great Depression was not a factor for wartime economic growth, since recent studies show that the Great Depression was ended by the end of World War II, not by the beginning of it.
