Final answer:
A complete sentence contains a subject and a predicate and expresses a complete thought. Sentence A "Vultures eat the remains of dead animals." is a complete sentence.
Step-by-step explanation:
A complete sentence contains a subject and a predicate and expresses a complete thought. In the given options, sentence A, "Vultures eat the remains of dead animals." is a complete sentence because it has a subject (Vultures) and a predicate (eat the remains of dead animals) and expresses a complete thought. Sentence B, "Flea medicine for our cats is expensive, we order it online." is not a complete sentence because it lacks a coordinating conjunction or a punctuation that separates the two independent clauses properly.