To solve this question, the user needs to have knowledge of basic cybersecurity concepts.

The correct answer is:

B. Accountability

Option A, Authentication refers to the process of verifying the identity of a user or system before granting access.

Option C, Authorization is the process of granting or denying access to specific resources or actions.

Option D, Nonrepudiation refers to the ability to prove that a particular action or event occurred and that it cannot be denied by the party who performed it.

Option B, Accountability is the ability to determine the actions and behaviors of a single individual within a system and to identify that particular individual. It is the answer to the question "who did what, when, and how" in a given system.

Therefore, the correct answer is B. Accountability.