Final answer:
In the process of implementing an amendment to the U.S. Constitution, the amendment must be ratified by at least three-fourths of the states to become law.
Step-by-step explanation:
The question refers to the process of how an amendment to the United States Constitution becomes law. For an amendment to be incorporated into the Constitution, it must be ratified by a specific number of states. The correct answer to the provided multiple-choice question is 'B. three-fourths'. This means that after the federal government proposes an amendment, at least three-fourths of the states must ratify the amendment for it to become effective. This process of ratification is guided by Article V of the Constitution. It is designed as such to ensure that any changes to the document have widespread support across the United States.