One of the pioneers of classical realism, Hans Morgenthau (1997) states six principles of realism that could help us comprehend profoundly the realist vision of international phenomenon. These six principles are:
1. Politics is governed by objective laws that have their roots in human nature.
2. Statesmen conduct themselves in terms of interest defined as power.
3. Interest determines political conduct within the political and cultural context which foreign policy is formulated.
4. Prudence is the supreme virtue in international politics. There can be no political morality without prudence.
5. Nations are entities that pursue their interests as defined by power and should not be judged by universal moral principles. 
6. Political realism rejects the legalistic-moralistic approach to international politics.

The correct answer is E.