The solution that an app builder should use to meet this requirement is master-detail relationship. A master-detail relationship is a type of relationship that creates a parent-child relationship between two objects, where the child records inherit the sharing and security settings of their parent record. The app builder can create a master-detail relationship between Supplier__c and SupplierItem__c objects, where Supplier__c is the parent object and SupplierItem__c is the child object. This way, when a Supplier__c record is deleted, all related SupplierItem__c records are also deleted automatically. Option A is incorrect because many-to-many relationship is not suitable for this requirement, as many-to-many relationship allows two objects to be linked in both directions through a junction object, but does not support cascading delete. Option B is incorrect because indirect lookup relationship is not suitable for this requirement, as indirect lookup relationship allows an external object to link with another object using an external ID field, but does not support cascading delete. Option C is incorrect because hierarchical relationship is not suitable for this requirement, as hierarchical relationship allows users to use a lookup field that links an object with itself, but does not support cascading delete.