Joseph Stalin, Franklin Roosevelt, and Winston Churchill met at the Tehran Conference in 1943. They were leaders of the Soviet Union, the United States, and the United Kingdom. During World War II these men were known as the "Big Three" because they led

A) the countries that suffered the most casualties during the war.

B) countries that had declared war on each other

C) the only countries fighting against Germany,

D) the most powerful of the Allied countries.