Final answer:
The complete subject of the provided sentence is "People from a variety of countries" and the complete predicate is "have been credited with the discovery of platinum." These comprise the main parts of the sentence structure.
Step-by-step explanation:
In the sentence "People from a variety of countries have been credited with the discovery of platinum," the complete subject is "People from a variety of countries" which denotes who the sentence is about. Meanwhile, the complete predicate is "have been credited with the discovery of platinum" since it includes the verb phrase and tells us what is being said about the subject.
To further breakdown the components of the sentence: "People" is the simple subject, "from a variety of countries" is a prepositional phrase that modifies the subject, and "have been credited with the discovery of platinum" is the predicate that contains the action or state of being regarding the subject.