The correct answer is C.
During the war, prosperity had already come back to the US after the depression times. The economy after the WWII experienced an impressive and sustained economic growth era which lasted until the 1973 recession. The US became the richest and most powerful country and economy in the world.
Growth was caused by several factors: the automobile industry, the housing boom, the increase in military and defense spending due to the arrival of the Cold War, the switching towards the focus on production of services rather than goods, working conditions had improved, gains in productivity for farmers,etc.