Can you use read replicas to improve the availability of your RDS database?
You can reduce load on your primary database instance by creating read replicas and directing read queries to them. However, a read replica can not be promoted to primary database instance (except in the case of Aurora).
You can configure Multi-AZ setup for your RDS to increase availability. With Multi-AZ, a standby copy of your database is kept in sync, and promoted to primary database if needed.
According to AWS exam terminology, a read replica improves performance, not availability.