A lookup relationship is a type of relationship that links two objects together, but does not affect security or deletion. It can be used to create a relationship between shipments and accounts where shipments should have a lookup to accounts; this way, shipments can show related account information on their records, but when an account is deleted, the shipments remain. Accounts should have a lookup to shipments is not a valid option because it does not match the requirement of seeing all shipment items from an account page; it would show related account information on shipment records instead. Shipments should have a master-detail to accounts or accounts should have a master-detail to shipments are not valid options either because they do not match the requirement of keeping shipments when an account is deleted; they would delete shipments along with their master account records. References: https://help.salesforce.com/s/articleView?id=sf.relationships_lookup.htm &type=5