Which solution should a data architect recommend a clean migration?

Universal Container is Implementing salesforce andneeds to migrate data from two legacy systems. UC would like to clean and duplicate data before migrate to Salesforce.

Which solution should a data architect recommend a clean migration?
A . Define external IDs for an object, migrate second database to first database, and load into Salesforce.
B. Define duplicate rules in Salesforce, and load data into Salesforce from both databases.
C. Set up staging data base, and define external IDs to merge, clean duplicate data, and load into Salesforce.
D. Define external IDs for an object, Insert data from one database, and use upsert for a second database

Answer: C