Tailgating attacks occur when an unauthorized individual slips into a facility behind an authorized user who opens the door. Air gaps are not sufficient on their own as someone can easily catch up with an authorized person as the door is opened. So this is not the correct answer. With biometrics, once one person has authenticated, another person can still slip in following the authorized person. So this is not the correct answer. Turnstiles may help with tailgating attacks, but an attacker could jump over the turnstile, making it not as effective. So this is not the best answer option either. Access control vestibules are isolation areas where one person completes the authentication process and accesses the facility before a second person can enter the vestibule. This is the correct answer.