How Did the Allied Campaign in Italy Prepare for the Ground

How did the Allied campaign in Italy prepare for the ground invasion of France on D-Day?

A) The defeat of Mussolini's regime forced Hitler to redirect valuable German troops to occupy Italy.
B) American soldiers had the opportunity to hone their fighting skills in the much more forgiving Mediterranean theater of war.
C) Allied forces had to secure the Mediterranean for unperturbed access to Middle Eastern oil, a necessary resource for the ground invasion.
D) By occupying Italy, Allied forces were able to channel supplies through Switzerland and France to the westward marching invaders from Normandy.