Returning to unanswered questions in quiz in Captivate 7

Hi!

Client needed a quiz with time limit. Now that it's done he also wants the learners to be able to skip difficult questions, so they can answer simple ones and then return to answering hard ones again.

I've added "Back" and "Next" buttons so learner can navigate between questions, but I can't figure out how to make it show only unanswered questions.

Could you please give any suggestions on solving this problem or maybe there is some workaround, that would ultimately get the job done?