If an organization has both Master-Detail and Lookup relationships established, what behavior can be expected regarding data sharing?

The correct reasoning for the answer regarding the behavior of data sharing in Master-Detail and Lookup relationships is rooted in the inherent characteristics of these relationships within Salesforce.

In a Master-Detail relationship, the child record's access is directly tied to the sharing settings of the parent record. This means that if a user has access to a parent record, they will automatically have access to all related child records. The sharing model is effectively hierarchical: the visibility or sharing settings of the parent record dictate the accessibility of the child records. This mechanism simplifies data management by ensuring that sharing permissions are consistently applied throughout related records.

In contrast, Lookup relationships do not establish such a dependency, allowing more flexibility regarding data access. Each object can have its own sharing settings independent of the other. While users can link records, the sharing permissions must be managed separately.

This distinction highlights why the answer indicating that Master-Detail relationships allow automatic sharing based on parent record visibility is accurate, as it describes the essential functionality of this relational type in Salesforce.