What defines a sentence?

A sentence is defined as a group of words that expresses a complete thought. This definition emphasizes the importance of both structure and meaning in language. A complete thought means that the sentence conveys a clear idea, which usually involves a subject and a predicate. This is crucial for effective communication, as it allows the reader or listener to understand precisely what is being expressed without ambiguity.

In contrast, other options lack the essential components of what makes a sentence meaningful. For instance, a phrase without a subject does not convey a complete thought, as it is incomplete and lacks the necessary structure for clarity. A single word describing an action may provide some information but fails to form a complete thought on its own. Lastly, a collection of random words does not adhere to grammatical rules or logic, making it impossible to convey coherent meaning. Thus, the correct answer highlights the fundamental role of complete thoughts in the construction of sentences.