You may ask exactly two questions, each addressed to only one person. They have to be yes-or-no questions.
[color:"#3A495A"]Ask D "IF A AND B ARE DIFFERENT, is A a truth-teller?"[/color]
But that isn't a yes-or-no quesiton. It's a yes-or-no-or-other question. By adding the condition, you force the posibility of a third answer: nothing or "A and B aren't different."
Although, I do like the answer you gave. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" /> It's jut a symantics thing. <img src="/ubbthreads/images/graemlins/tongue.gif" alt="" />
