Which 2 data archiving strategies should a data architect recommend?

Universal Containers (UC) requires 2 years of customer related cases to be available on SF for operational reporting. Any cases older than 2 years and upto 7 years need to be available on demand to the Service agents. UC creates 5 million cases per yr.

Which 2 data archiving strategies should a data architect recommend? Choose 2 options:
A . Use custom objects for cases older than 2 years and use nightly batch to move them.
B . Sync cases older than 2 years to an external database, and provide access to Service agents to the database
C . Use Big objects for cases older than 2 years, and use nightly batch to move them.
D . Use Heroku and external objects to display cases older than 2 years and bulk API to hard delete from Salesforce.

Answer: C,D