Universal Containers has created two custom objects called Seminars and Attendees. Organization- wide defaults for these objects have been set to…

The junction object is on the detail side of two master-detail relationships with the Seminars and Attendees objects. In a master-detail relationship, the detail record (the junction object record) inherits its sharing and security settings from its master records.

Since the Organization-Wide Defaults (OWD) for both master objects are Private, users must first be granted at least Read access to the specific Seminar and Attendee records they need to connect. An owner-based sharing rule is the appropriate mechanism to grant this access to the select group of users (B).

Next, the master-detail relationship itself has a Sharing Setting. By setting this to Read Only, you allow users who have only Read access to the master records to create and edit the related detail (junction) records, provided their profile or permission set grants them create/edit permissions on the junction object itself (A).

C. Lookup filters are used to restrict which records can be selected in a relationship field for data integrity purposes; they do not grant record access or permissions.

D. An object on the detail side of a master-detail relationship cannot have its own sharing rules, as its access is exclusively controlled by the master record(s).

1. Salesforce Help & Training, "Master-Detail Relationship Considerations": This document explicitly states, "Custom objects on the detail side of a master-detail relationship can't have sharing rules... The detail and subdetail records inherit the sharing and security settings from the master record." This directly invalidates option D.

2. Salesforce Help & Training, "Create a Master-Detail Relationship": In the field creation wizard, the "Sharing Setting" property is defined. The help text for this setting clarifies its purpose: "Choose the minimum access level to the master record required to create, edit, or delete detail records." The Read Only option allows a user with only read access on the master to modify the detail record, supporting the choice of option A.

3. Salesforce Security Guide, "Sharing Rules" (Page 38): This guide details the function of sharing rules: "Sharing rules represent the exceptions to your organization-wide default settings... Use sharing rules to grant users access to records they don’t own..." This supports using a sharing rule (Option B) to grant access to the master records when the OWD is Private.