It would be natural to have N/A -option available for many questions. My own example is sliders, something like

Do you like following foods:

Tomatoes: |---o--| [ ] Have never eaten tomatoes
Potatoes: |-o----| [ ] Have never eaten potatoes

but I think most question types should have this possibility. I know that this can be done by JS-workaround or by splitting the question, but first one is hard to use for a non-nerd and second is somewhat unnatural to the user answering the survey.