Marketing solution

Marketing solution

What should a data architect recommend that would help upgrade uniquely identify customer across multiple systems:
A . Store the salesforce id in all the solutions to identify the customer.
B . Create a custom object that will serve as a cross reference for the customer id.
C . Create a customer data base and use this id in all systems.
D . Create a custom field as external id to maintain the customer Id from the MDM solution.

Answer: D