Which solution meets these requirements?

Explanations:

Amazon Elastic File System (EFS) provides scalable file storage that can be mounted simultaneously on multiple EC2 instances. It offers built-in redundancy and is designed for high availability, making it ideal for storing core company assets like client case files that need to be accessed concurrently by multiple applications.

Amazon Elastic Block Store (EBS) provides block-level storage that can only be attached to a single EC2 instance at a time. While it is durable and redundant, it does not meet the requirement for simultaneous access from multiple servers.

Amazon S3 Glacier Deep Archive is primarily designed for long-term data archiving and is not suitable for frequent access or immediate availability of files. It also lacks the necessary features for concurrent access by multiple applications.

AWS Backup is a service that automates backup tasks across AWS services but does not provide a storage solution itself. It does not meet the requirement for simultaneous access to files by multiple application servers.