Which of the following is used to allow or deny access to network resources?

NFS (Network File System) is a distributed protocol for sharing files across a network - it enables file access but is not itself a mechanism for allowing or denying general network resource access.

System hardening is a security process of reducing attack surface by disabling unnecessary services and applying patches - it improves security posture but is not a resource access control mechanism.

An ACL is a rule-based list applied to network interfaces, file systems, or services that evaluates traffic or access requests against criteria such as source IP, destination port, or protocol, then permits or denies accordingly. ACLs are foundational to both network perimeter control (router/firewall rules) and resource-level access management. They directly fulfill the definition of allowing or denying access to network resources.

Spoofing is an offensive attack technique where an attacker forges an identity (IP, MAC, email) to impersonate a legitimate entity - it is an attack, not an access control countermeasure.