Which set of licence types will enforce username uniqueness across all Salesforce organisations and Communities?

Universal Containers will be implementing several Communities, and wants to ensure login uniqueness.

Which set of licence types will enforce username uniqueness across all Salesforce organisations and Communities?
A . Partner Community and Lighting External Apps Plus
B . Customer Community, Customer Community Plus, and Lightning External Apps
C . Lightning External Apps Plus and Lightning External Apps
D . Customer Community and Partner Community

View Answer

Answer: B