I have some data that is not frequently accessed. But when requested within six months, the data needs to be available immediately. After six months, the data is not accessed but needs to be maintained for historical purposes. What is the best S3 storage class lifecycle available to me with the lowest possible cost?

Answer options:

A.Store data for the first 6 months in S3 Standard & move data to Glacier after that.
B.Store data the first 6 months in S3 One Zone – IA & move data to Glacier after that.
C.Store data the first 6 months in S3 Standard IA & move data to Glacier after that.
D.Store data in Glacier & use expedited retrieval for accessing data immediately.

Answer: B
On analyzing the scenario carefully, we can see here that data is infrequently accessed for the first 6 months & is then archived for long term storage.
Option A is incorrect since it is not advisable to store data in S3 Standard that is not frequently accessed. S3 standard will incur higher costs for this scenario.
Option B is CORRECT. S3 One Zone IA offers the best cost-effective solution for infrequently accessed data. Since the lowest cost is desired here, we can overlook the resilience model offered by High Availability storage solutions. After six months, data can be moved to Glacier for archival purposes.
Option C is incorrect. S3 Standard IA is more cost-effective than its S3 standard counterpart for infrequently accessed data. But we do not select it as the best available option compared to the pricing of S3 One Zone IA, which offers a 20% subsidized cost compared to S3 Standard IA.Option D is incorrect because Glacier offers a way to store archival data rather than storing it for frequent/infrequent access. Also, expedited retrieval costs are greater (0.03 per GB) than the S3 One Zone IA cost which is 0.01 per GB.References: 
https://aws.amazon.com/s3/storage-classes/
https://aws.amazon.com/s3/pricing/
https://youtu.be/wYclDu6GhkU