What distinguishes prescriptive doctrine from descriptive doctrine?

The correct choice highlights a key characteristic of prescriptive doctrine, which is that it outlines specific directives and rules that are meant to be followed precisely. This type of doctrine provides clear guidelines and standards for actions, emphasizing adherence to established procedures without deviation. In this context, "must be followed exactly" denotes the rigid framework that prescriptive doctrine provides, ensuring that operations or tasks are executed consistently and in alignment with predetermined guidelines.

On the other hand, descriptive doctrine serves a different purpose; it describes practices, concepts, and ideas that are observed in the field but does not enforce strict compliance. Therefore, while it may be valuable for understanding best practices and operational experiences, it allows for a more flexible approach and adaptation based on situational needs. The distinction lies in how strictly each type must be adhered to, with prescriptive doctrine requiring exact compliance compared to the more adaptable nature of descriptive doctrine.