The correct answer is C. Network latency.
The diagram shows a solution that uses synchronous replication between two remote protection domains, cluster site A and cluster site B. Synchronous replication is a feature that allows near-zero RPO (recovery point objective) by replicating data to the remote site before acknowledging writes to the local site. However, synchronous replication has some requirements and limitations that must be met for it to work properly. One of these requirements is that the network latency between the two sites must be less than or equal to 5 ms1. If the network latency is higher than 5 ms, the synchronous replication will fail and the protection policy will be suspended2.
Therefore, based on the diagram, the most likely cause of the issue is that the network latency between cluster site A and cluster site B is higher than 5 ms, which prevents the synchronous replication from working. To verify this, the administrator can use the "ncli cluster ping" command to measure the network latency between the two sites3. If the network latency is indeed higher than 5 ms, the administrator can either improve the network performance or switch to a different replication mode, such as near-synchronous or asynchronous.