After having failed his exam, a student goes and confronts his lecturer about it.
Student: “Sir, do you really understand anything about the subject?”
Professor: “Surely I must. Otherwise I would not be a professor!”
Student: “Great, well then I would like to ask you a question. If you can give me the correct answer, I will accept my mark as is and go. If you however do not know the answer, I want you to give me an “A” for the Exam.”
Professor: “Okay, it’s a deal. So what is the question?”