Option B is the right answer that the war in Europe was already nearly won by this time because its priority was to help its allies first defeat the Nazis.
Europe first was the principal factor of the grand strategy on which the U.S and U.K agreed during the World War II. The main motive of this policy-making was that the U.S and the U.K would use their resources to defeat Nazi Germany.
The declaration of war from Germany on the United States in 1941 and the direct attack of Japan on the Pearl Harbor in America directed America to face a decision on how to allocate its resources between these two different threats. Therefore, the United States joined Europe first to deal with Japan and Germany respectively.
