Which solution meets these requirements?

Explanations:

Enabling Multi-AZ deployment for the DB instance provides high availability and automatic failover to a standby instance in a different Availability Zone, ensuring a low RPO. In Multi-AZ, the primary DB instance is synchronously replicated to a standby instance, which allows for an RPO of less than 1 second.

Enabling auto scaling for the DB instance in one Availability Zone does not address the need for high availability or data redundancy. Auto scaling only manages the number of instances based on demand, which does not provide an RPO of less than 1 second.

Configuring the DB instance in one Availability Zone with read replicas in a separate Availability Zone may improve read performance, but it does not ensure an RPO of less than 1 second for the primary database. Read replicas are asynchronously replicated, so there can be significant lag, leading to a higher RPO.

Configuring the DB instance in one Availability Zone and using AWS DMS for change data capture (CDC) tasks does not provide an RPO of less than 1 second for the primary database. CDC typically involves a delay in capturing changes, which does not meet the stringent RPO requirement.