This one doesn't rank so high on the list because it's been around for a while, and they toyed with this question in The Name Of The Doctor. Still, one has to ask, will we actually get an answer to this question this time around? After all, it is "The Fall of The Eleventh", and we are visiting Trenzalore again. Though come to think of it, why is it that "no living creature can speak falsely or fail to answer"? Is Trenzalore the universe's leading supplier of Truth Serum? Or perhaps there is a special circumstance that will render the populace at such odds that they want The Doctor off of their planet, so they'll eschew protecting him. If this were true, what's to say that an acquaintance, or dare we say a Companion, wouldn't feel the same way and feel inclined to rat out The Doctor's biggest secret? This is one of those issues Moffat just has to resolve before moving on to the Capaldi era, and he did say that the episode will carry a lot of resolution to questions that have been in play for a while. Let's hope he answers this one creatively enough that while we probably won't get an answer, we'll get something much better out of the deal: closure.