Final answer:
The annotated document pertaining to 'key control' is most likely associated with reviewing the adequacy of control processes within an organization.
Step-by-step explanation:
The document with annotations saying "key control" followed by a brief explanation and recognized as belonging to the staff internal auditor probably pertains to the activity of reviewing the adequacy of control processes. This activity involves assessing if the controls in place are suitable for their intended purpose, ensuring that they are capable of effectively managing risks that the organization may face.
This process typically includes reviewing documentation, understanding how control activities are supposed to work, and making annotations or recommendations, as seen on the sales contract form mentioned.