Final Answer:
The purpose of this document on usability testing is C. To provide an explanation of and guidelines for conducting usability testing.
Step-by-step explanation:
The document's primary aim is to offer an explanation of usability testing and provide guidelines for its implementation. Option C captures the essence of the document's intent, emphasizing the need for clarity and guidance in understanding and executing usability testing processes. Usability testing is a crucial aspect of website development to ensure user-friendliness and effectiveness.
While option B touches on promoting usability testing, it doesn't encompass the comprehensive approach of explaining and guiding as outlined in option C. Options A, D, and E don't align with the broader objective of providing insights and guidelines for usability testing; instead, they focus on narrower or unrelated goals.
Option C is the answer.