Question navigation feature?

[CruiseDevice]

There should be functionality where user can navigate through questions. Why can't user come back to previous question once answered? What if he wants to change the response afterwards. There must also be a timer to keep track of quiz. I tried implementing it using cookies, and it works fine. Only thing is when timer runs out, (and as the remaining questions are not answered), then the answer paper is not generated. It returns KeyError.