Visitors entering a building are required to close the back door before the front door of the same entry room is open. Which of the following is being described?

Tailgating is the attack that a mantrap is designed to prevent - it describes an unauthorized person following an authorized person through a secure door.

Fencing is a perimeter security barrier placed around the outside of a facility, not an entry room with interlocking doors.

Screening refers to the process of inspecting or verifying individuals, not a specific physical access control mechanism with interlocking doors.

A mantrap (also called an airlock or sally port) is an entry system with two doors that cannot be open simultaneously - the first door must fully close and often the person must be authenticated before the second door unlocks. This design physically prevents unauthorized individuals from following an authorized person through a secured entry. The scenario described matches the mantrap definition exactly.