Which additional combination ofAWS services will meet these requirements with the LEAST administrative effort?

Explanations:

Amazon EC2 provides virtual servers in the cloud, but it requires more administrative effort for setup, scaling, and maintenance compared to serverless options.

AWS Lambda is a serverless compute service that automatically scales and manages the infrastructure, requiring minimal administrative effort. It can be integrated with API Gateway and can utilize RDS for relational data storage.

Amazon RDS is a managed relational database service that simplifies the setup, operation, and scaling of a relational database, minimizing administrative tasks for managing backups, patching, and replication.

Amazon DynamoDB is a NoSQL database service, which does not support relational data requirements. While it is managed and scalable, it does not meet the requirement for a relational data format.

Amazon EKS is a managed Kubernetes service that requires more operational overhead for managing containerized applications. It involves configuring and managing clusters, which adds to administrative effort compared to serverless solutions.