Which amendment is the only one in the history of the united states that was ratified by state conventions rather than state legislatures?

a) amendment 26
b) amendment 24
c) amendment 21
d) amendment 22

Congress passed the 21st Amendment in February 1933. It was ratified by a series of state conventions rather than by state legislatures, which have been used to ratify every other amendment, as Congress felt that many state legislators remained beholden to pro-Prohibition interests