But then you're implying that you'll get a correct answer 1/2 of the time, which means that the answer is B, but then the answer is correct only 1/4 of the time, and you've got yourself in an infinite loop.
1/4^2 divided by 2 = 1/32 (The odds of picking the correct answer twice in two attempts) and so on..... the more you try the less chance you have of succeeding so just give up and cheat off the guy next to you. I made this crap up so what's the chance of it being right? a)0% b)0^ c)what he wrote d)no chance