The correct answer is C) Moscow.
The capital city of an allied power during World War II was Moscow.
Moscow is the capital city of Russia, one of the Allied powers during World War II. Rome is the capital city of Rome, and during World War II, Italy was part of the Axis, supporting Germany. Vienna is the capital city of Austria, and Stockholm is the capital city of Sweden, and both countries were not part of the Allied powers during World War II.