The correct answer is A) France.
The invasion you are talking about is known by several terms including: Storming of Normandy, D-Day, Operation Overlord, etc.
This event saw the largest amphibious invasion in military history. This plan was lead by US General Dwight D. Eisenhower. This was considered a turning point in World War II, as the Allied Powers were able to now liberate Europe from Nazi control. Along with this, the Allied powers freed roughly 200,000 prisoners of war in Europe.