This option is the most efficient because it uses AWS DataSync, which is a secure, online service that automates and accelerates moving data between on-premises and AWS Storage services1. It also uses DataSync to transfer large amounts of data back and forth between NFS file systems in the two Regions on a periodic basis, which simplifies and speeds up the data transfer process with minimal operational overhead. This solution meets the requirement of transferring large amounts of data back and forth between NFS file systems in the two Regions on a periodic basis with the least operational overhead. Option B is less efficient because it uses AWS Snowball devices, which are physical devices that let you transfer large amounts of data into and out of AWS2. However, this does not provide a periodic data transfer solution, as it requires manual handling and shipping of the devices. Option C is less efficient because it sets up an SFTP server on Amazon EC2, which is a way to provide secure file transfer protocol (SFTP) access to files stored in Amazon S33. However, this does not provide a periodic data transfer solution, as it requires manual initiation and monitoring of the file transfers. Option D is less efficient because it uses AWS Database Migration Service (AWS DMS), which is a service that helps you migrate databases to AWS quickly and securely. However, this does not provide a data transfer solution for NFS file systems, as it only supports relational databases and non-relational data stores.