Which type of cluster should the database specialist create to meet these requirements?

Explanations:

Amazon ElastiCache for Memcached is a memory caching service for use cases that require low latency but does not support advanced data structures like sorted sets or ACID-compliant transactions.

Amazon Neptune is a fully managed graph database service that is optimized for graph data models and is not suitable for high-performance in-memory operations on advanced data structures such as sorted sets.

Amazon ElastiCache for Redis is a fully managed, in-memory key-value store that supports advanced data structures like sorted sets and provides sub-millisecond latency for reads and writes. It also supports transactions, including ACID-compliant operations, and can be backed up for cluster recovery.

Amazon DynamoDB Accelerator (DAX) is a fully managed, highly available, in-memory cache for DynamoDB but is not designed to support advanced data structures like sorted sets, and does not offer the level of control required for ACID-compliant operations.