Students in a certain class take CET-6. Regarding the results of the examination, there are the following guesses? A? All people have passed. B? The squad leader failed. C? Someone must have failed. Ding? Not everyone will fail. If only one of the above guesses is untrue, then the following is true? ['A guessed wrong and the squad leader failed.', 'B guessed wrong and the squad leader passed.', 'C guessed wrong, but the squad leader passed.', 'Ding guessed wrong and the squad leader failed.']