The least privilege principle requires that each subject in a system
be granted the most restrictive set of privileges (or lowest clearance) needed for the performance of authorized tasks. The application of this principle limits the damage that can result from accident, error, or unauthorized use. Applying this principle may
limit the damage resulting from accidents, errors, or unauthorized
use of system resources.
*Answer "A formal separation of command, program, and interface functions." describes separation of privilege, which is the separation of functions, namely between the commands, programs, and interfaces implementing those functions, such that malicious or erroneous code in one function is prevented from affecting the code or data of another function.
*Answer "A combination of classification and categories that represents the sensitivity of information." is a security level. A security level is the combination of hierarchical classification and a set of non-hierarchical categories that represents the sensitivity of information.
*Answer "Active monitoring of facility entry access points." is a distracter. Source: DoD
5200.28-STD Department
of Defense Trusted Computer System Evaluation Criteria.

By technical controls we mean some or all of the following: Access Control software Antivirus Software Passwords Smart Cards Encryption Call-back systems Two factor authentication

The correct answer is "The * (star) Integrity Axiom".
Answers a and d are distracters. Answer the Simple Integrity Axiom states, Asubject at one level of integrity is not permitted to observe (read) an object of lower integrity (no read down).