Are you surprised by the correct answer? This is a nice question, but I don't think you can say there is only one "correct" answer, at least in a grammatical sense. Subjunctive mood is never grammatically necessary. It just allows you to better express subtleties. It is a great advantage to know how to use it well but it is, after all, a "mood", and nobody can insist that you display a certain mood. I do like the question, but I would have asked for the "best answer" rather than the "correct answer". If you omit "high", the correctness of the other answer becomes apparent.

Are you surprised by the correct answer?

But what does it mean?

Are you surprised by the correct answer?

Are you surprised by the correct answer?