Final answer:
The most common way to amend the United States Constitution is through proposal by a 2/3 majority of Congress and approval by 3/4 of state legislatures.
Step-by-step explanation:
The most common way to amend the United States Constitution is option A - Proposal by a 2/3 majority of Congress, approval by 3/4 of state legislatures. To propose an amendment, two-thirds of both chambers of Congress must agree to the proposal. Then, the amendment must be ratified by three-fourths of the state legislatures. This process has been used for the majority of the twenty-seven amendments that have been added to the Constitution.