Which 2 solutions should a data architect recommend in order to minimize performance and storage issues?

UC has millions of Cases and are running out of storage. Some user groups need to have access to historical cases for up to 7 years.

Which 2 solutions should a data architect recommend in order to minimize performance and storage issues? Choose 2 answers:
A . Export data out of salesforce and store in Flat files on external system.
B. Create a custom object to store case history and run reports on it.
C. Leverage on premise data archival and build integration to view archived data.
D. Leverage big object to archive case data and lightning components to show archived data.

Answer: C,D