The right answer is D. Baron de Motesquieu.
Montesquieu's theory of separation of powers, on which most modern Western states are based, affirms the distinction between the three powers (executive, legislative and judicial) and their mutual limitations. For example, in a parliamentary democracy, the legislature (Parliament) limits the power of the executive (government): it is not free to act at will and must constantly secure the support of Parliament, which is the expression of the will of the people. In the same way, the judiciary allows counterbalancing certain governmental decisions.