The answer is controlled by runtime behavior, not by naming similarity. Choose A. Create owner-based sharing rules that give Read access to the master objects.; C. Set Sharing Settings to Read Only on both Master-Detail relationship fields. The requirement in the stem is: Universal Containers has created two custom objects called Seminars and Attendees. Organization-wide defaults for these objects have been set to Private. Universal Containers wants to set up a new junction object. The selected option addresses that requirement at the point where Salesforce actually evaluates the behavior.
The underlying concept is record sharing targets. Manual record sharing can grant access to individual users, public groups, and roles with subordinates. It is a record-level access mechanism, separate from field-level security and permission set assignment. That is why this answer is more defensible than a workaround. It can be reviewed in Setup, included in the correct deployment path, and tested by impersonating or logging in as a representative user where appropriate.
The other options fall short for clear platform reasons. B (Set lookup filters on both junction object relationship fields.) handles a different concern; A lookup relationship is more loosely coupled and does not provide every master-detail behavior, especially native roll-up behavior. D (Create an owner-based sharing rule that gives Read access to the junction object.) should be rejected because Sharing controls record visibility; it does not change field type, page composition, or automation timing. Before release, test the configuration with the affected profile and realistic records, not only with a system administrator account.
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