The correct answer is letter D.
Explanation: A nation-state is a historical area that can be identified as having a legitimate policy, which by its own means constitutes a sovereign government. While a state is a political and geopolitical entity, a nation is an ethnic and cultural unit.
The word empire means a large territory, contiguous or not, composed of several different nations, and which is dominated by a nation that imposes its will on others economically and militarily. The supreme leader of an empire is called the emperor.