Once an amendment is formally proposed, how long do the States have to ratify it?

A. There is no time limit on the ratification process and States have as long as they wish to consider amendments.
B. States must ratify an amendment within seven years of Congress voting to propose that amendment.
C. Congress has the power to set a varying time limit for ratifying each amendment as long as it is reasonable.
D. If an amendment is not ratified within one year, it goes back to Congress, which must vote to approve it again.