Answer:
c. 2/3 vote by both houses of Congress; d. 2/3 vote by both houses of Congress
Step-by-step explanation:
The Constitution provides that an amendment may be proposed either by the Congress with a two-thirds majority vote in both the House of Representatives and the Senate (more common) or by a constitutional convention called for by two-thirds of the State legislatures.
Article V of the Constitution prescribes how an amendment can become a part of the Constitution. While there are two ways, only one has ever been used. All 27 Amendments have been ratified after two-thirds of the House and Senate approve of the proposal and send it to the states for a vote.