What are the 3 key actions that should be done when data modeling in salesforce?

UC has a legacy client server app that as a relational data base that needs to be migrated to salesforce.

What are the 3 key actions that should be done when data modeling in salesforce? Choose 3 answers:
A . Identify data elements to be persisted in salesforce.
B. Map legacy data to salesforce objects.
C. Map legacy data to salesforce custom objects.
D. Work with legacy application owner to analysis legacy data model.
E. Implement legacy data model within salesforce using custom fields.

Answer: A,B,D