Final answer:
During D-Day, the Allied forces faced two main challenges: poor weather and stiff German resistance. The unexpected weather conditions complicated the landing operations, while the entrenched German defenses led to significant casualties among the invading troops. The correct option is C.
Step-by-step explanation:
The two most difficult challenges faced during D-Day were poor weather conditions and stiff German resistance. Operation Overlord, commonly known as D-Day, commenced on June 6, 1944, under challenging circumstances. The preparation for the invasion had to take into account the unpredictable English Channel weather, which played a critical role in the timing of the operation. Although the poor weather caught the Germans by surprise, it also created difficulties for the Allied forces, such as rough seas and visibility issues. Nevertheless, this did not prevent the landing of approximately 156,000 troops across the Normandy beaches.
The second significant challenge was the German defenses entrenched along the Normandy coast. The Germans fortified the coastline with obstacles, mines, and gun emplacements, which the Allies faced during the amphibious landings. The presence of experienced German troops and the strategic placement of their defense installations led to a high number of casualties on the Allied side. Despite these challenges, the Allies were able to establish beachheads and push onward, eventually leading to the liberation of Paris and contributing to the defeat of Nazi Germany.