Somebody voices exactly that, and Ibiki smiles. "You see, there's more special rules - if you choose not to, your points will be dropped to zero, and both you and your two teammates will fail the test. But if you choose to take the question and answer incorrectly, that person will be unable to enter the chunin selection exams again!"
"What kind of stupid rule is that?" one of the Leaf genin protests. "Plenty of people have taken this exam before!"
Ibiki starts to chuckle, then - "You guys got unlucky. I wasn't the proctor before; this year it's my rules. But I'm giving you an out - just choose not to, and you'll be able to try again next time." He pauses for people to digest that, then continues with, "And now let's begin the tenth question! Those who choose not to take it, raise your hand. Once your number is confirmed, leave."
There's a long moment of silence, then someone raises his hands, apologizing to his teammates. Slowly, people start to trickle out.