A developer needs to build and deploy a serverless application that has an API that mobile clients will use. The API will use Amazon DynamoDB and Amazon OpenSearch Service (Amazon Elasticsearch Service) as data sources. Responses that are sent to the clients will contain aggregated data from both data sources.
The developer must minimize the number of API endpoints and must minimize the number of API calls that are required to retrieve the necessary data.
Which solution should the developer use to meet these requirements?

A. GraphQL API on AWS AppSync
B. REST API on Amazon API Gateway
C. GraphQL API on an Amazon EC2 instance
D. REST API on AWS Elastic Beanstalk