You have been given a business requirement to retain log files for your application for 10 years. You need to regularly retrieve the most recent logs for troubleshooting. Your logging system must be able to store the given large volume of logs. What cost-optimized technique should you use to meet these requirements?

Answer options:

A.Store your log in Amazon CloudWatch Logs.
B.Store your logs in Amazon Glacier.
C.Store your logs in Amazon S3, and use lifecycle policies to archive to Amazon Glacier.
D.Store your logs on Amazon EBS, and use Amazon EBS snapshots to archive them.

Correct answer is
C.Option A is invalid, because although it can store the large volume of logs, it is NOT a "cost-optimized technique" that the question asks for.
Option B is invalid, because it won’t server the purpose of regularly retrieve the most recent logs for troubleshooting. 
Option D is invalid, because it is not an ideal storage option.
You can define lifecycle configuration rules for objects that have a well-defined lifecycle. For example:
If you are uploading periodic logs to your bucket, your application might need these logs for a week or a month after creation, and after that you might want to delete them.
Some documents are frequently accessed for a limited period of time. After that, these documents are less frequently accessed. Over time, you might not need real-time access to these objects, but your organization or regulations might require you to archive them for a longer period and then optionally delete them later.
You might also upload some types of data to Amazon S3 primarily for archival purposes, for example digital media archives, financial and healthcare records, raw genomics sequence data, long-term database backups, and data that must be retained for regulatory compliance.
 For more information on Lifecycle management please refer to the below link:
http://docs.aws.amazon.com/AmazonS3/latest/dev/object-lifecycle-mgmt.html