Reference: IIA Business Knowledge for Internal Auditing, Inventory Valuation section.

Reference: IIA Business Knowledge for Internal Auditing, Physical Security Controls section.

Comprehensive and Detailed In-Depth Explanation:
Primary controls in spreadsheet management focus on ensuring data accuracy, integrity, and security.
Option A (Locking formulas and static data) prevents unauthorized changes, ensuring data integrity. This is a direct control over spreadsheet accuracy, making it the correct answer.
Option B (Backup storage) is an IT operational control, not a primary financial reporting control.
Option C (Documentation of spreadsheet use) is important for governance but does not directly prevent errors.
Option D (Version control software) helps manage changes but does not directly ensure financial reporting accuracy.
Thus, locking and protecting spreadsheet formulas is the most critical primary control for accurate financial reporting.
Reference: IIA IT Controls & Data Governance