Hello.
The most suitable answer is c) the Red Army's capture of Berlin. Even though, I must say that the Battle of Stalingrado and the D-Day invasions were important to the outcome of the Second World War too but the capture of Berlin meant the surrender of Germany.
The Battle of Berlin. also known as The Fall of Berlin, was fought on April 16th, 1945 culminated in the Soviet victory, the suicide of Adolf Hitler and other Nazi officials, the inconditional surrender of Berlin, and marked the end of the war.
Hope this helps
