A chief audit executive assigns a team of three internal auditors to carry out an...

Comprehensive and Detailed Explanation:

The scope of an engagement defines the boundaries of the audit — what areas, functions, activities, or processes will be reviewed. In this case, the engagement’s purpose is to test adherence to the procurement policy, so the sub-processes (D) within procurement (e.g., vendor selection, purchase approvals, invoice processing) should be clearly defined in scope.

Sample size (A) and procedures (C) are part of the audit work program, not scope.

Inherent risks (B) are identified during planning but do not define scope boundaries.

Therefore, Option D is correct: defining sub-processes ensures that the audit scope is comprehensive and appropriately focused on procurement policy adherence.