Final answer:
A complete sentence is one that expresses a complete thought and contains both a subject and a predicate. Option A is a complete sentence, while option B is a sentence fragment.
Step-by-step explanation:
A complete sentence is a sentence that expresses a complete thought and contains both a subject and a predicate. A subject is who or what the sentence is about, while a predicate is what the subject is doing or what is being said about the subject. In this case, option A, Made pancakes and baked corn muffins for our breakfast on Sunday morning, is a complete sentence because it has a subject 'Made' and a predicate 'pancakes and baked corn muffins for our breakfast on Sunday morning'. Option B, All living things on Earth contain the element carbon, is not a complete sentence because it is missing a subject, making it a sentence fragment.