Checks and balances are instated by a government to limit the amount of power a branch has on another by giving the other branches the ability to "check" and act on the other for a fair government. International relations would deal with standings with other countries, nations, or kingdoms, while executive veto is the power of the President to deny any bill that has been passed. But since this example doesn't describe Wilson vetoing anything, it can't be C. Rule of law is saying that anyone, no matter how much power, wealth, title or status you have, everyone is bound to the law. The option left is D, because the Senate is "limiting" the authority of the executive branch (a president and his cabinet) by refusing to approve the Versailles Treaty. And that's why Wilson and America didn't join the League of Nations.
