GoBack option

I'm looking to input answer choices for an intelligence test in a questionnaire file, however, we want to give participants the choice to go back and change their answers before their time expires. Does anyone know what I can do so that the original answer choice a participant makes is still visible to the participant when they choose to GoBack and change their answer? Thanks!!

There currently isn't a way to do this; however the 2010 version of ML (being released this Fall) will have this option available.
You may be able to do a work around by using responses.xls; however this solution would only allow for the question to denote which answer was previously selected, rather than keep it pre-selected.