I don't know the stats specifically, but the answers generally weren't placed at random. In my head, that would likely make the first and last answer the least likely (outside of the last answer being all or none of the above). Thus, the middle answers are more likely to be selected for the correct answer. "C" then naturally allows you to read more answers. My unsupported two cents anyways.

Well, classically the fourth dimension is time (height, depth, width, and time would be how you plot where something is in space and time). Which you can't see time, so there's that.

But on the general nature of perception, you can only see within a narrow bandwidth of light, and there are colors outside your perception (like ultraviolet and infrared as a very immediately outside the band examples). You can't see radio waves, radiation, etc. The same is true for each other sense you have. Thus, it's "possible" an entire world that we can't perceive exists.