I believe "one correct answer" is here used with the meaning of "only one" and I thought this wasn't enough clear in Italian, so I added the word "sola" (only) to the translation. I deduced this meaning from the context: it's a quiz, so probably all the given options will be wrong, except for one. I then changed the word "revocare" with "annullare" in traslating "revoke" because I think it sounds less solemn and therefore it suits the context better.