The correct answer is D.
The system of Checks and Balances is a mechanism established in the US to preserve the principle of division of powers at the federal goverment level. The principle of division of powers states that the power of the state has to be divided in three independent branches: legislative (Congress), executive (government) and judiciary (court system).
A system to preserve the balance between the branches needs to be implemented, so that none of the branches gathers enough power as to overrule the others. For example, the Supreme Court has the power of judicial review, through which it can overturn laws passed by the Congress or goverment actions, if such practices are considered to be unconstitutional.