Final answer:
In Pega systems, pyDefault invokes pySetFieldDefaults through the inheritance structure, which allows a class to inherit rules and properties from its parent classes.
Step-by-step explanation:
In the context of Pega systems, pyDefault is a special rule that is used to set default values for properties when a new case is created. It can invoke pySetFieldDefaults, which is a data transform used for setting default field values. The component that enables pyDefault to invoke pySetFieldDefaults is d) Inheritance Structure. In Pega, inheritance allows a class to inherit properties, rules, etc., from its parent class(es). Therefore, the inheritance structure is what facilitates the invocation of one rule by another within a Pega application, adhering to the rules of inheritance defined in the application's class structure.