Identify the incomplete sentence.

The correct answer identifies an incomplete sentence, which is often referred to as a fragment. This particular example, "While they were sleeping," does not present a complete thought. It introduces a dependent clause that suggests there is more information to follow; however, it lacks an independent clause to complete the idea.

To be complete, a sentence needs to express a full thought that can stand on its own. In contrast, the other options provided are all complete sentences, conveying full ideas. "He wept" is straightforward and complete; "Everything worked out all right" clearly communicates a full sentiment; and "Babies are sure cute and cuddly" presents a complete thought about babies.