How are the EBS snapshots saved on Amazon S3?

Answer is B

http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EBSSnapshots.html

You can back up the data on your EBS volumes to Amazon S3 by taking point-in-time snapshots. Snapshots are incremental backups, which means that only the blocks on the device that have changed after your most recent snapshot are saved. This minimizes the time required to create the snapshot and saves on storage costs. When you delete a snapshot, only the data unique to that snapshot is removed. Active snapshots contain all of the information needed to restore your data (from the time the snapshot was taken) to a new EBS volume.

B.
Incrementally