Oh, of course. That's what I'm asking, though. If you say "if there's a clearly defined answer, then it's not an eternal question," that means that no matter how many answers you have (one or many), it's no longer an eternal question, as long as the answers are clearly defined. Because the emphasis (the way I read it at least) is on "clearly defined."
But if you mean for the emphasis to be on a, as in, only one single clearly defined answer can make this question not eternal, then of course you can't have many answers, no matter how clearly defined they are, or it's still an eternal question. With many possible answers.
Clearly, I did not define my point well enough. The general gist of your second paragraph matches what I was saying: that in order for the label "eternal" to no longer apply, there must be one chosen answer, no matter how clearly that answer is defined.
However, I would have to say that the word "answer" is an ambiguous one. Can the 20 candidates for the answer to the eternal question still be referred to as "answers"?