Which feature of Amazon RDS provides the ability to automatically create a primary database instance and to synchronously replicate data to an instance in another Availability Zone?

Explanations:

Read replicas are used for scaling read operations and do not provide synchronous replication.

Blue/green deployment is a strategy for minimizing downtime during application updates, not for database replication.

Multi-AZ deployment automatically creates a primary instance and synchronously replicates data to a standby instance in another Availability Zone.

Reserved Instances are a pricing model for reserving capacity and do not involve replication or high availability features.