Elasticity is the correct answer because it refers to the ability of the system to adapt to workload changes by provisioning and de-provisioning resources in an autonomous manner to match the demand as closely as possible. High availability ensures that services are accessible in the event of component failures, but it doesn't directly address scaling for demand. Global reach is more related to the presence of AWS around the world, and cost savings are a consequence of using Cloud services, not a benefit describing the dynamic scaling of the resources.