Which AWS service provides a hybrid storage solution that gives on-premises environments access to virtually unlimited cloud-backed storage?

AWS Storage Gateway is the correct answer because it is a hybrid cloud storage service that connects an on-premises software appliance with cloud-based storage, enabling seamless integration of on-premises applications with AWS storage services. It provides file, volume, and tape gateway options, allowing on-premises environments to access virtually unlimited cloud-backed storage. AWS DataSync is incorrect because it is a data transfer service that simplifies, automates, and accelerates moving data between on-premises storage systems and AWS storage services, but it doesn't provide ongoing hybrid storage access. Amazon S3 Glacier is incorrect because it is an archival storage service for data with infrequent access, not a hybrid solution for active on-premises integration. Amazon Elastic Block Store (Amazon EBS) is incorrect because it provides block-level storage volumes for use with Amazon EC2 instances, not a hybrid solution for on-premises environments.