Comprehensive and Detailed Explanation:

While several items listed are important parts of an overall engagement package, the authorization letter (often called written authorization, engagement letter, or authorization to test) is mandatory before testing begins — it explicitly grants permission to test specified systems under defined scope and constraints and provides legal protection for both parties. An RoE typically references or attaches the NDA (A), includes escalation/contact processes (B), and provides target lists (C), but without the formal authorization letter the engagement should not proceed.

CompTIA PT0-003 Mapping:

Domain 1.0 Planning and Scoping — obtain written authorization and define rules of engagement prior to testing.

===========