Which storage option should a solutions architect recommend?

Explanations:

Amazon S3 is an object storage service designed for scalability, but it does not support NFS, making it unsuitable for consistent and mountable shared storage needed by the build server.

Amazon FSx provides fully managed Windows file systems and is ideal for workloads requiring Windows-based file shares. It is not designed for NFS-based Linux environments, which the build server requires.

Amazon Elastic Block Store (EBS) provides block-level storage that is attached to a single instance. It does not support simultaneous access from multiple instances, making it unsuitable for a shared storage requirement across an Auto Scaling group.

Amazon Elastic File System (EFS) offers a fully managed NFS file system that can be mounted across multiple EC2 instances, making it ideal for applications requiring shared file storage. It provides consistent and scalable storage, meeting the requirements of the build server.