A complete sentence consists of a Subject and:

A complete sentence fundamentally requires a Subject and a Predicate. The subject is the noun or pronoun performing the action or being described, while the predicate contains the verb and all its modifiers, objects, or complements, describing what the subject does or is.

• Predicate is correct because it completes the essential structure of a sentence by providing the action or state of being for the subject.
• Adjective is incorrect; an adjective modifies a noun but is not a core structural component of a sentence.
• Article is incorrect; articles (a, an, the) are a type of adjective and do not form the predicate.
• Phrase is incorrect; a phrase is a group of words without a subject-verb pair and cannot stand alone as a complete predicate.