Lookup is the type of relationship that would be set up to meet the specification of pairing experienced Realtors with new Realtors. According to the Salesforce documentation, “A lookup relationship creates a loose association between objects. The lookup field allows users to select a record from another object.” Indirect lookup is used for junction objects on different platforms. Many-to-many is not a type of relationship, but a result of using junction objects. Master-detail is used for creating parent-child relationships.