How should an Identity Architect solution this requirement with limited custom development?

They would like to provide a single login for their partners.

How should an Identity Architect solution this requirement with limited custom development?
A . Create a partner login for the country of their operation and use SAML federation to provide access to other orgs.
B. Consolidate Partner related information in a single org and provide access through Salesforce community.
C. Allow partners to choose the Salesforce org they need information from and use login flows to authenticate access.
D. Register partners in one org and access information from other orgs using APIs.

Answer: A