Which of the following sentences illustrates the definition of a simple sentence?

A simple sentence is defined as a sentence that contains a subject and a predicate and expresses a complete thought. The sentence "My cat sleeps quietly in the corner." meets this definition perfectly. It has a clear subject ("My cat") and a predicate that describes an action ("sleeps quietly in the corner"). It conveys a complete thought independently, without any dependent clauses.

The other options do not qualify as simple sentences. For example, the second option contains multiple clauses introduced by "while," indicating that there are two actions happening simultaneously, thus making it a complex sentence. The third option features two independent clauses linked by "and," which categorizes it as a compound sentence. The fourth sentence also presents a dependent clause introduced by "although," making it another example of a complex sentence. Thus, the first option stands out as the only simple sentence in the set.