Answer:
Correct answer is C. It would cause Hitler to divert troops from the Russian front, thus weakening their advances there.
Step-by-step explanation:
Option C is the only correct answer as the Operation Barbarossa was under way and it was presenting a real threat for the Soviets, who fought under heavy casualties. The opening of new front made situation easier for them.
Option A is not correct as that could not happen without new fronts in Europe.
B is not correct as most of the army was attacking Soviet Union.
D is not correct as this could not happen without Operation Overlord.