I think the choices are the following:
A. Powers and duties of the United States government are divided among three branches of government.
B. Powers and duties of the United States government are decided by a system of direct democracy.
C. Powers and duties of the United States government are chosen entirely by the President of the United States.
D. Powers and duties of the United States government are divided among two branches of government.
two of those options describe separation of powers: A and D, but D does it better: in fact the powers are divided into three branches, not two: Judicial, Executive and Legislative.
