Which one of the following methods was used only once to ratify an amendment?

A. By approval of conventions in three-fourths of the states

B. By approval of the Supreme Court

C. By approval of three-fourths of the state legislatures

D. By approval of the President

The correct answer is A. By approval of conventions in three-fourths of the states

The most common way is the third one, three-fourths of state legislatures and a supermajority of the congress approves it, however, only once the first method was used. It is a legitimate option outlined in the constitution. The congress can call for national conventions which can pass the amendment but this doesn't happen often.