"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

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

The main purpose of the excerpt is to explain how the Constitution maintains a necessary partition of power among the branches of government by establishing a system of checks and balances. The example provided in option C best illustrates this concept, as it shows how the judiciary branch can check the powers of the legislative branch by declaring a law unconstitutional.