The project team requires an AWS service that provides a filesystem simultaneously mounted from different instances of EC2. Which AWS service will satisfy this requirement?

Answer options:

A.Amazon EFS
B.Amazon S3
C.Amazon EBS
D.Amazon FSx for Windows File Server

Answer: A
Option A is CORRECT. Amazon EFS is a regional service storing data within and across multiple Availability Zones (AZs) for high availability and durability. You can access your file systems across AZs and regions. You can also share files between thousands of Amazon EC2 instances and on-premises servers via AWS Direct Connect or AWS VPN.
Option B is INCORRECT. Amazon Simple Storage Service (Amazon S3) is an object storage service that offers industry-leading scalability, data availability, security, and performance.
Option C is INCORRECT. Amazon Elastic Block Store (Amazon EBS) provides persistent block storage volumes for Amazon EC2 instances in the AWS Cloud.
Option D is INCORRECT. Amazon FSx for Windows File Server provides a fully managed native Microsoft Windows file system so you can easily move your Windows-based applications that require file storage to AWS.
 Reference:
https://docs.aws.amazon.com/whitepapers/latest/aws-overview/storage-services.html