Final answer:
Data Courier prevents duplicate CIDs by assigning a unique identifier to each CID, preventing duplicates at the point of creation or addition to the system.
Step-by-step explanation:
Data Courier ensures that there are no duplicate CIDs in the system by using a unique identifier for each CID. This identifier is typically managed by a database system that automatically checks for uniqueness when a new CID is created or added to the system. By using unique identifiers, the system is essentially built to prevent duplicates from occurring in the first place.
Option 2, regularly checking for duplicate CIDs and removing them, would be a reactive approach, which is less efficient than prevention. Option 3, encrypting the CIDs, could provide security but would not necessarily prevent duplicates. Lastly, option 4, restricting access to the CID database, can help maintain data integrity but does not directly prevent duplication.