Exam Certified Platform App Builder topic 1 question 159 discussion

Here's the confusing part of the question. You cannot CREATE a master-detail relationship with a standard field as the detail. However, there are some M-D relationships that exist where a standard object is the detail. Oppty & Oppty Product for example.

All true, all the answers quote the exact SF documentation. https://help.salesforce.com/s/articleView?id=sf.workflow_field_update_considerations.htm&type=5

For all custom objects and some standard objects, you can create workflow and approval actions where a change to a detail record updates a field on the related master record. Cross-object field updates work for custom-to-custom master-detail relationships, custom-to-standard master-detail relationships, and a few standard-to-standard master-detail relationships. For more information, see Cross-Object Field Updates on page 11. https://help.salesforce.com/s/articleView?id=sf.workflow_field_update_considerations.htm&type=5

Correct answer shouldn't be C? You can't have a custom to standard master-detail relationship, not sure about the A option though.