Which AWS service should the company use?

Explanations:

Amazon DynamoDB is a fully managed NoSQL database service that provides single-digit millisecond performance at any scale. While it supports data storage and retrieval, it is not specifically an in-memory data store. Instead, it is a persistent database solution.

Amazon ElastiCache is a fully managed in-memory data store compatible with Redis and Memcached. It is designed for cloud-based environments and provides fast data access, making it ideal for use cases like caching, session management, and real-time analytics. Its compatibility with open-source technologies makes it the best choice for in-memory data storage.

Amazon Elastic Block Store (EBS) provides block storage for use with Amazon EC2 instances. While it is used for data storage, it is not an in-memory data store and does not provide the low-latency access that in-memory stores do.

Amazon Redshift is a fully managed data warehouse service designed for big data analytics. While it is efficient for querying large datasets, it is not an in-memory data store and focuses on disk-based storage and complex querying rather than in-memory processing.