What Was the Greatest Single Advantage That the United States

What was the greatest single advantage that the United States and its Allies had during World War II?

A) The Allies began military confrontations with the Axis powers immediately, before they could gain much ground in Europe or Asia.
B) The Allies were genuinely willing to work together to defeat their enemies, whereas the Axis powers fought separate wars.
C) The Germans and Japanese made slow progress in conquering more lands in Europe and the Pacific.
D) All of the Axis powers suffered from ineffective leadership and poor strategizing.
E) The Allies had such an overwhelming number of ground troops that Axis resistance was highly ineffective.