A master-detail relationship fromEngineering_Support__ctoOpportunityallows multiple childEngineering_Support__crecords to be associated with a single parentOpportunity. It also enables roll-up summary fields to aggregate data from the child records onto the parentOpportunity. Reference:Master-Detail Relationships Incorrect Options: A & D:Lookup relationships do not support roll-up summary fields. C:Master-detail cannot go in the opposite direction (Opportunity to Engineering_Support__c) for this use case.