The correct answer is B.
OBJ-1.5: An access control vestibule, or mantrap, is a device that only allows a single person to enter per authentication. This authentication can be done by RFID, a PIN, or other methods. Once verified, the mantrap lets a single person enter through a system, such as a turnstile or rotating door. CCTV will not stop piggybacking, but it could be used as a detective control after an occurrence. Wearing security badges is useful, but it won’t stop piggybacking by a skilled social engineer. RFID badges may be used as part of your entry requirements, but it won’t stop a determined piggyback who follows an employee into the building after their authenticated RFID access has been performed.