Verified Answer :

Allies had to fight a two-front war because they were
fighting the Germans in Europe and Africa while they had to contend with the
Japanese in Asia.  They had to distribute
their resources evenly to maintain the fight in these fronts.  Fortunately, the Russians fought Germany in East
while the Allies made a push to Germany after D-Day.

Answer:

d. supplying the troops across a huge part of the globe

Explanation:

edge 2021