Which AWS service provides a POSIX compliant, fully managed and cost-effective NFS file storage solution?

Answer options:

A.Amazon FSx for Windows File Server
B.AWS Elastic File System
C.Amazon FSx for Lustre
D.Amazon Elastic Block Store

Answer: B
Option A is INCORRECT. Amazon FSx for Windows File Server is built for windows server and is accessible over SMB protocol.
Option B is CORRECT. EFS is a POSIX compliant, fully managed and cost-effective NFS file storage solution that could be used with both on-prem and AWS resources.
Option C is INCORRECT. Amazon FSx for Lustre provides storage for compute workloads. Amazon FSx for lustre is a fully managed high-performance and cost-effective storage.
Option D is INCORRECT. Amazon Elastic Block Store is a block storage solution and not an NFS file storage solution.
Reference:
https://aws.amazon.com/fsx/windows/
https://aws.amazon.com/efs/
https://aws.amazon.com/fsx/lustre/
https://aws.amazon.com/ebs/