1) There can be no solution, since the ambiguity of ‘correct’ makes the question ill-posed.
It's true the question is ambiguous, but this still seems a bit of a cop-out.
2) There is no solution.
This seems to take this interpretation of the question.
Which answer (or set of answers) of “p%”, is such that the statement ‘the probability of picking such an answer is p%’ is true?
Then this appears to be a well-posed question, but there is no solution.
3) 0%.
Consider a different interpretation of the question.
Is there a p%, such that the statement ‘the probability of picking an answer “p%” is p%’ is true?
Then this appears a well-posed question and has the solution p = 0, even though this is not one of the answers. Of course if answer C) were changed to “0%” (as it is in this 2007 version of the question ), then this would also have no solution.
4) We can produce any answer we want by changing the probability distribution for the choice.
Why should ‘random’ mean an equally likely chance of picking the 4 answers? If we, say, assume the probabilities of choosing (A) (B) (C) (D) to be (10%, 20%, 60%, 10%) then the answer to either formulation (2) and (3) is now “60%”. But if we make the distribution (12.5%, 15%, 60%, 12.5%) then we seem to back to square one again, since there is now both a 25% chance of picking “25%”, and a 60% chance of picking “60%”.
I like conclusion 3) best, ie 0%.