How can the Administrator ensure that the bucket is only accessible to members of the Administrator’s AWS account?

Explanations:

Moving an S3 bucket to a private subnet is not applicable, as S3 buckets do not exist in a subnet within a VPC; S3 is a globally accessible service, and this option does not affect access control.

Changing the bucket access control list (ACL) to restrict access to the bucket owner ensures that only the account that owns the bucket can access it, effectively preventing access from users in other AWS accounts.

Enabling server-side encryption for objects in the bucket protects the data at rest but does not affect access permissions to the bucket itself. This does not restrict access to users outside of the administrator’s account.

Using presigned URLs allows temporary access to objects in the bucket, but it does not restrict access to the bucket itself; users with presigned URLs can still access the bucket if they are not properly restricted.