When taking a multiple choice test, the old adage comes to mind: 'When in doubt, Pick C'.
It turns out that this is true in many cases. On a multiple choice test, with four solutions, the middle two choices tend to be the most correct answers. This presents a Gaussian (normal) distribution for the choices A, B, C, and D. Why do you think this is?
This explains why "when in doubt, pick C" has some validity.