Which of the following is NOT a remark but a restriction in the CAS brief?

In a Close Air Support (CAS) brief, restrictions are specific limitations or constraints placed on the operations, while remarks provide additional information. The area of operations, known as the Airspace Coordination Area (ACA), is considered a restriction. It delineates where the air support can operate and where specific coordination measures must take place to ensure safe engagement of targets.

Conversely, specifics such as type of ordinance, time on target, and target description are typically aspects of the brief that provide essential details on how the mission should be executed but do not necessarily impose restrictions. Instead, they serve to enhance the understanding and clarity of the operation.

Thus, recognizing that an ACA is fundamentally a restriction guiding the operational parameters of CAS makes it clear why this is the correct choice in identifying a restriction rather than a mere remark in the CAS brief.