Which setup allows for data extensions to be used by child business units in a...

Shared Data Extensions in Salesforce Marketing Cloud allow data extensions to be accessible across multiple business units within an account. This setup enables parent and child business units to access and use the same data extensions, facilitating data consistency and shared marketing efforts across the organization.

Why Not Salesforce or Synchronized Data Extensions: Salesforce Data Extensions are used for CRM data, and Synchronized Data Extensions are for syncing with Salesforce objects. Shared Data Extensions are explicitly designed for sharing data across business units.

Salesforce Documentation Reference: Refer to Shared Data Extensions for further details.