Which of the following best describes a sentence?

A sentence is best defined as a set of words that is complete in itself, conveying a statement or question. This definition captures the essential components that make a sentence functional and meaningful. A sentence typically includes a subject and a predicate, allowing it to convey a complete thought or idea. For example, "The cat sleeps" is a complete sentence because it gives a clear idea of what is happening, with an identifiable subject (the cat) and a predicate (sleeps).

In contrast, the other choices do not provide an accurate depiction of what constitutes a sentence. A collection of unrelated words does not form a cohesive meaning, and an incomplete thought lacks the necessary structure typically required for a full sentence. Furthermore, a mere string of words that lacks grammatical structure fails to convey a coherent idea or message. Therefore, the option that accurately describes a sentence is the one that highlights its completeness and ability to express a thought, making it the correct choice.