Montesquieu is credited with devising the basic constitutional principle of
a) natural rights.
b) popular sovereignty.
c) separation and balance of governmental power.
d) government was created by man for his own purposes.

Correct  C) separation and balance of government power.

In his book, The Spirit of the Laws (1748), Montesquieu outlined how different forms of government work in different situations.  He looked at how despotic governments function on the basis of fear of the ruler.  Systems built around monarchy and aristocracy function on the basis of the principle of honor, as persons of rank strive for higher honor and position.  In republics, Montesquieu identified "love of virtue" as the key principle -- where individuals are willing to put the interests of the whole society ahead of their own individual interests.

Within his treatment of how governments will function best, Montesquieu argued that executive, legislative, and judicial functions of government ought to be divided between parts of the government, so that no one person or division of the government can infringe on the overall rights of others in the government or of the members of the society overall.