The correct statement is:
The reference monitor concept is today's access control list.
The reference monitor concept refers to a security mechanism that enforces access control policies by validating and authorizing requests from subjects to objects. It acts as a trusted component within a computer system that mediates all accesses and ensures that they comply with the specified security policies.
Access control lists (ACLs) are a common implementation of the reference monitor concept in modern operating systems. They provide a list of permissions associated with each object, specifying which subjects are allowed or denied access to the object.
While audit logs and file systems are important components of a secure system, they are not synonymous with the reference monitor concept or access control lists. Audit logs record system events for monitoring and forensic purposes, and file systems manage the storage and organization of files on a computer.