Which MDM data element is needed to allow reporting across these systems?

UC has the following system:

✑ Billing system.

✑ Customer support system.

✑ CRM system.

US has been having trouble with business intelligence across the different systems. Recently US implemented a master data management (MDM) solution that will be the system of truth for the customer records.

Which MDM data element is needed to allow reporting across these systems?
A . Global unique customer number.
B. Email address.
C. Phone number.
D. Full name.