What is access control?

A.
A method of ensuring that a subject (user, program, or process) is the entity itclaims to be

B.
Requiring the subject to provide a second piece to the credential set, as in a password, passphrase, cryptographic key, or token

C.
Security features that control how users and systems communicate and interact with other systems and resources

D.
Controlling how an active object accesses a passive subject

Explanation:
Access controls are security features that control how users and systems communicate and interact with other systems and resources. They protect the systems and resources from unauthorized access and can be components that participate in determining the level of authorization after an authentication procedure has successfully completed. Access is the flow of information between a subject and an object. A subject is an active entity that requests access to an object or the data within an object. A subject can be a user, program, or process that accesses an object to accomplish a task. When a program accesses a file, the program is the subject and the file is the object. An object is a passive entity that contains information.