My suggestion is the ability to have multiple questions displayed on the registration form.
That said, I think a nice feature with the questions and answers would be to allow the admin to set (example here) a hundred questions though when it comes to displaying them on the registration form a random generator kicks in and displays them. 100 questions on a registration form is too much I hear you say? They'll also need to be an input field in the admincp where the admin can input a value (say 3) but 3 questions will appear on the reg form. All this will be random generated from the 100 questions in the list you set earlier.