According to the IIA's Code of Ethics, internal auditors are responsible for maintaining their knowledge, skills, and other competencies at a level required to perform their professional responsibilities2. Internal auditors should also pursue relevant professional development opportunities to enhance their ability to add value to the organization3. Therefore, option C is the correct answer.
The other options are not correct. The officer in charge of human resources, the chief audit executive, and the CEO may support or facilitate the internal auditor's professional development, but they are not ultimately responsible for it4. The internal auditor has the primary accountability and obligation to maintain and improve their own competencies5.