Glad to see a primarily objective category system in a poll. I find it difficult to vote in polls where the options aren't distinct.
By the way I'm guessing things like Iceland / Svalbaad and any of the other mid oceanic islands belong to the continent of the primary tectonic plate they are on.
Iceland is in both North America and Europe, geologically speaking. The tectonic plates meet there. You can actually stand with one foot in each continent.
So it is still possible you might need to pick two options in this poll.