which is a complete sentence? his story about an unexpected alien invasion. celery, onions, and carrots…

Brief Explanations:

A complete sentence needs a subject and a predicate (a verb and a complete thought). The first option "His story about an unexpected alien invasion" is a phrase (noun phrase with a prepositional phrase) and lacks a verb, so it's not a complete sentence. The second option "Celery, onions, and carrots compose the French mirepoix, a base for soups and sauces" has a subject (Celery, onions, and carrots), a verb (compose), and a complete thought (explaining what they compose and what mirepoix is), so it's a complete sentence.

Answer:

Celery, onions, and carrots compose the French mirepoix, a base for soups and sauces.