Have you considered making some of your answers required. Additionally there is a "Allow to resume" feature which allows survey respondents to finish the survey in more than one setting.
...answers when you need them
In the take survey page the respondent should have the option of seeing unanswered question. As we understand, typically when the users take a survey, they forget to answer few questions and based on the further set of questions the user may get some data for filling the answer for a question which he/she have left before. So providing an option would help the end user to track which all questions he left unanswered.
Apart from this the survey administrator should be given a option to say whether the option should be available for the respondents or not.
This would help for long survey or surveys which have too many things to respond.
Have you considered making some of your answers required. Additionally there is a "Allow to resume" feature which allows survey respondents to finish the survey in more than one setting.