The answer to that is the Native Americans.
Based from the diary entry, it would seem as though the Germans were ready for the Americans to attack. They put mines and obstacles in the sea and on land to deter the approaching army. They used a German 88mm gun-- a long-range anti-air craft, anti-tank, anti-personnel gun most feared by the Allies-- to gun down American soldiers.
Despite these diffulties, the American soldiers drew inspiration and strength to continue fighting under the leadership of Gen. Theodore Roosevelt Jr., son of President Theodore Roosevelt, one of the highest-ranking officer on the beach during D-day
I believe the answer is A, Pollution of the environment, hope this helps :)
