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.
adeadman 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.