The correct answer is D.
The federal government of the United States is the national state of the United States, is constituted under the theories of separation of powers, therefore it is divided into three distinct branches: legislative, executive and judicial, whose powers are conferred by the Constitution of the United States.
Each branch has its own exclusive competence and powers that allow them to limit the actions of the other two branches and together the three branches have total sovereignty given by the United States Constitution.