How did the Soviet’s win at Stalingrad help advance the Allies’ Europe First strategy?

How did the Soviet’s win at Stalingrad help advance the Allies’ Europe First strategy?
A. It prompted several Axis countries in Eastern Europe to switch their allegiance.
B. It enabled the Soviets to push the eastern front toward Germany.
C. It consolidated Soviet power in Russia.
D. It removed the German threat on the war’s eastern front.