"to what expedient then, shall we finally resort, for maintaining in practice the necesary partition of power among the several departments, as laid down in the constitution? the only answer that can be given is 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."

- james madison, federalist paper #51

which of the ideas incorporated in the united states constitution is expressed in the question above?
a) judical review
b) direct democracy
c) checks and balances
d) the powers of the three branches of government