The correct answer is option 2, the theory of checks and balances. This is because the requirement for Senate ratification of appointments made by the President and treaties signed by him demonstrates a system of checks and balances in the U.S.A. Under the theory of checks and balances, the government is divided into separate branches, each with its own powers and responsibilities. This ensures that no single branch of the government becomes too powerful. In this case, the requirement for Senate ratification ensures that the President`s appointments and treaties are subject to scrutiny and approval by another branch of the government, the legislative branch represented by the Senate. This helps to prevent abuse of power and provides a system of accountability and oversight. The other options are not the correct answer because they do not directly refer to the specific mechanism of Senate ratification in relation to appointments and treaties.