Amazon DynamoDB and Amazon Elastic File System (Amazon EFS) are the correct choices because both services are Regional by design and provide built in high availability across multiple Availability Zones without extra configuration.

Amazon DynamoDB is a fully managed NoSQL database that automatically spreads data and traffic across multiple Availability Zones in a region to provide low latency and high durability without the customer having to configure multi AZ replication.

Amazon Elastic File System (Amazon EFS) offers a managed, elastic file system that can be accessed from instances in multiple Availability Zones and the service handles replication and failover so the file system is available across AZs by default.

Amazon Elastic Block Store (Amazon EBS) replicates data within a single Availability Zone and attaches to instances in that zone which means it does not provide default multi AZ availability without additional services or architecture changes.

Subnet is an Availability Zone scoped network construct and therefore a single subnet cannot by itself provide regional high availability. You must place resources in multiple subnets across AZs to achieve resilience.

Instance Store storage is ephemeral and physically tied to the host for a single instance in one Availability Zone so it is not durable or available across zones and cannot provide built in regional high availability.

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