Final answer:
The sentence 'until the popcorn finishes popping' is a dependent clause because it contains both a subject and a verb but cannot stand alone as a complete sentence.
Step-by-step explanation:
The sentence in question, "until the popcorn finishes popping," is not a complete sentence on its own but a group of words. To determine whether it is a phrase or a clause, we need to identify if it has both a subject and a verb. The word 'until' is a subordinating conjunction, which typically introduces a dependent clause. A dependent clause has both a subject and a verb, while a phrase lacks one or the other. In this case, "the popcorn" is the subject, and "finishes popping" is the verb phrase. Therefore, the group of words is a dependent clause because it cannot stand alone as a complete sentence and relies on an independent clause to complete its meaning.