Answer:
I remember, in college, reading a study where someone took tens of thousands of multiple-choice tests from different disciplines and studies. The result was that, on a standard 4-choice test, the letter "C" came up more than 28% of the time as an answer.
This was due to "writer's bias," and the author assumed it was because the letter "C" - or the third choice - would "be hidden" as a selection.
A small deviation from 25%, sure, but now, as a high-school teacher and an Ohio graduation test-prep tutor, I tell my kids that, if they come across a question where they absolutely can't use deduction and/or find an educated guess (e.g., "What is the capital of Mongolia?" with 4 similar answers), to pick the letter "C" - you have at least a 1 in 4 chance of being right, and if you consistently pick "C" in these circumstances (hopefully only once or twice per test!), you have a slightly mathematically higher chance of getting that question right... maybe only a fraction higher, but at that point, "Play the numbers!"