Which type of sentence contains a subject and a predicate but does not express a complete thought?

A sentence fragment is a type of sentence that contains a subject and a predicate but does not express a complete thought. This means that while it may have the basic components that form a sentence, it lacks the necessary information to stand alone as a complete idea. For example, a fragment might be something like "When we went to the store," which leaves the reader expecting more information about what happened next.

In contrast, a complete sentence provides a full thought and can stand alone. A run-on sentence improperly connects two or more independent clauses, while a complex sentence includes at least one independent clause and at least one dependent clause. Thus, the key characteristic of a sentence fragment is its inability to convey a complete thought, making it clear why this option is the correct answer.