Final answer:
In Salesforce, the custom field types available for a child object in an external object relationship are Lookup Relationship, Indirect Lookup Relationship, and External Lookup Relationship.
Step-by-step explanation:
In the context of Salesforce and external object relationships, the custom field types available for a child object are:
- Lookup Relationship
- Indirect Lookup Relationship
- External Lookup Relationship
A Lookup Relationship is a standard field type that links one object to another in Salesforce. An Indirect Lookup Relationship is a custom field type that links an external object to a standard or custom object based on a corresponding value. Lastly, an External Lookup Relationship is a custom field type that links an external object to another external object.
The Master-Detail Relationship and Hierarchical Lookup Relationship are not valid options for external object relationships. The Master-Detail Relationship creates a tight relationship with cascade-delete and roll-up summary fields, while the Hierarchical Relationship is specific to user objects, for creating user hierarchies.
The correct answer is Lookup Relationship, Indirect Lookup Relationship, External Lookup Relationship.