Which storage option is both cost-efficient and scalable?

You are building an automated transcription service in which Amazon EC2 worker instances process an
uploaded audio file and generate a text file. You must store both of these files in the same durable storage until
the text file is retrieved. You do not know what the storage capacity requirements are. Which storage option is
both cost-efficient and scalable?

A.
Multiple Amazon EBS volume with snapshots

B.
A single Amazon Glacier vault

C.
A single Amazon S3 bucket

D.
Multiple instance stores