The correct answer is A. The threat of American military action.
Definition: The most relevant of the Roosevelt Corollary is not the Big Stick policy, without the sophistication that implies the control of the own citizens, in principle, and of the rest, later, by means more subtle that the club in the head. No, what gives character to that document is that Roosevelt says, literally, that the US should intervene, as a world policeman, wherever it is necessary to fight, not an infringement of human rights, no, but a relaxation of the rules of the civilized society. Textually he said:
"If a nation demonstrates that it knows how to act with reasonable efficiency and decency in social and political matters, if it maintains order and pays its obligations, it does not need to fear any intervention from the United States".
