The best answer is B. Senior management.
The culture that supports an effective internal control system is set from the top. ISACA's governance and culture guidance consistently treats culture as a management and leadership responsibility. Senior leadership establishes tone, values, expectations, accountability, and behavioral norms that shape how controls are designed, followed, and enforced across the enterprise. A strong control culture depends on visible commitment from leadership, not just procedural ownership by operational teams.
Option A. HR supports the culture through hiring, training, and policy reinforcement, but HR does not have primary accountability for the overall control environment.
Option C. Line management plays an important role in day-to-day control execution, but enterprise culture is primarily driven by senior leadership.
Option D. Internal audit evaluates and provides assurance over the control system; it does not own or establish the control culture because doing so would impair independence.
Therefore, B is the correct answer because senior management is primarily accountable for establishing the tone and culture that enable an effective and efficient internal control system.
References (Official ISACA):
* ISACA Journal, Auditing Your Organizational Culture.
* ISACA Now Blog, Culture as a Corporate Asset.
* ISACA Digital Video/Podcast, Understanding and Assessing Organization Culture.
* ISACA Journal, Auditing Culture.

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