The correct answer is Mechanical door locks.

Mechanical door locks are a physical access control that directly prevents people from entering a facility without permission by creating a tangible barrier that must be unlocked with a key or credential. They are implemented at entrances and other points of access and are a primary example of a physical security control.

Cloud Identity and Access Management is incorrect because it is an identity and access management solution for digital resources and cloud services rather than a physical barrier that stops people from walking into a building.

Background screening for staff is incorrect because it is an administrative control used to vet personnel and reduce insider risk and it does not physically prevent unauthorized individuals from entering a facility on its own.

Firewall rules in a virtual private cloud are incorrect because they are network or technical controls that filter traffic to and from virtual networks and they do not provide a physical means to block people from entering a site.

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