Which of the following is NOT one of the four principles of WCAG?

The correct choice is C, which identifies "Feasible" as not one of the four principles of the Web Content Accessibility Guidelines (WCAG). The four established principles—Perceivable, Operable, Understandable, and Robust—serve as a foundational framework for creating accessible web content.

Perceivable means that information and user interface components must be presented to users in ways that they can see or hear. Operable refers to ensuring that users can interact with the interface; it must be navigable and functional through various means (e.g., keyboard, mouse). Understandable emphasizes that both the information presented and the operation of the interface must be clear and comprehensible. Lastly, Robust indicates that content should be compatible with various user agents and assistive technologies so that it is accessible over time and adaptable to future technologies.

Feasibility, while an important concept in broader project management and development contexts, is not specifically defined as one of the core principles of WCAG. This distinction reinforces the importance of focusing on the established principles to guide web accessibility efforts effectively.