A ____________ uses PPLI receptions to maintain and improve synchronization.

The correct answer is that a Primary User (PRU) utilizes PPLI (Position, Purpose, Lawful Interception) receptions to maintain and improve synchronization. In the context of Link 16 operations, the PRU plays a central role in managing network synchronization by receiving PPLI data, which provides essential information about the positional and operational status of network participants.

PPLI receptions are critical for ensuring that all users within the network are aligned in terms of timing and operational intent, which enhances the overall effectiveness of the joint operations. This synchronization is vital for maintaining the integrity and accuracy of communications and situational awareness among the various units engaged in the mission.

Other choices, while relevant to Link 16 and joint operations, do not specifically reference the role of PPLI receptions in maintaining synchronization as directly as the Primary User does. The Network Time Reference, for instance, serves to standardize time across the network but does not directly handle the operational data from multiple users. Secondary Users and Link 16 terminals have their specific functions but are not primarily responsible for the synchronization provided through PPLI information.