"TO WHAT expedient, then, shall we finally resort, for maintaining in practice the necessary partition of power among the several departments, as laid down in the Constitution? The only answer that can be given is, that as all these exterior provisions are found to be inadequate, the defect must be supplied, by so contriving the interior structure of the government as that its several constituent parts may, by their mutual relations, be the means of keeping each other in their proper places."

Use the passage to answer the question.
What is the main purpose of this excerpt from The Federalist No. 51, and which of the following best illustrates it?
A.
to outline the powers of the executive branch; the president signs a treaty
B.
to outline the powers of the legislative branch; Congress changes the date of an election
C.
to outline the system of checks and balances among the three branches; the Supreme Court declares a law unconstitutional
D.
to outline the system of checks and balances among the three branches; the president announces that he will run for a third term

C. to outline the system of checks and balances among the three branches; the Supreme Court declares a law unconstitutional

The main purpose of this excerpt from The Federalist No. 51 is to discuss the system of checks and balances among the three branches of government in order to maintain the necessary partition of power as laid down in the Constitution. The example of the Supreme Court declaring a law unconstitutional best illustrates this concept of one branch of government keeping the others in check.