The MOST effective control for addressing the risk of piggybacking is:

A. a single entry point with a receptionist.

B. the use of smart cards.

C. a biometric door lock.

D. a deadman door.

Explanation:

Deadman doors are a system of using a pair of (two) doors. For the second door to operate, the first entry door must close and lock with only one person permitted in the holding areA. This reduces the risk of an unauthorized person following an authorized person through a secured entry (piggybacking). The other choices are all physical controls over entry to a secure area but do not specifically address the risk of piggybacking.