Comprehensive and Detailed Step-by-Step Explanation:

Reference to IIA Standards:

Standard 1110 - Organizational Independence: The chief audit executive (CAE) must report functionally to the board to ensure independence.

The audit charter must define the CAE’s functional reporting line to the board, securing protection from undue management influence.

Reasoning:

Option C addresses the foundational document—the audit charter—that establishes the CAE’s authority and independence.

Option A refers to operational standards, but they do not directly safeguard against interference.

Option B strengthens governance but is secondary to the audit charter in securing independence.

Impact:

A robust audit charter formalizes the CAE’s reporting relationship and ensures organizational independence, empowering internal audit.