The sentence is a complete and correct sentence. Option A is correct.
A complete sentence is made up of three elements: a subject, verb, and an object. The subject is usually a noun or a pronoun. Besides, since there's a subject, there will be a verb due to the fact that all verbs need a subject. What is more, the object of a sentence is the element that acts upon by the subject. Moreover, sometimes commas play an importal role in a complete sentence.
Think this? A society organized for the purpose of waging war. Sparta became a state because they were scarred by the emerging threat of a helot revolt.
