d. three-fourths . . . two-thirds
Both the Congress and state legislature can propose an amendment: The Senate and the House of the U.S. Congress can propose it by at least two-thirds of votes in favor, and the state legislature also can do it by calling a National Convention first, in which two-thirds of votes has to be on favor of proposing it.
After this, the amendment has to be ratified; depending on who proposed it, it is only ratified with at least three-fourths of the state legislatures or both houses of Congress.
