Some guy who had a game show that created a mathematical paradox.
On 7/22/15, Purple Drank, Lobo, bay_of_puigs and Pyramids debated: If you were taking a test with three answers, and you chose A, and the teacher told you B was wrong, should you switch to C?
This led to Pyramids (under the alias pyramidchode) creating a post on the popular website, Reddit, in their Math and AskScience sections, in order to settle the debate. Surprisingly, Pyramid's post garnered tons of attention on Reddit. It received over 1200 upvotes and even very briefly made an appearance at the bottom of the front page, which is extremely difficult to do.
Ultimately, the correct answer is that unless the teacher knew you had chosen A, it does not matter if you switch or not.