Which of the following is an example of a compound sentence?

A compound sentence is defined as a sentence that contains at least two independent clauses connected by a coordinating conjunction, such as "and," "but," or "or." The example that illustrates this perfectly is the selected answer, which states, "She studied hard, and she passed the exam."

In this sentence, there are two independent clauses: "She studied hard" and "she passed the exam." Each clause could stand alone as a complete sentence; therefore, linking them with the coordinating conjunction "and" creates a compound sentence. This structure allows for a more complex expression of ideas by combining two related thoughts into one cohesive statement.

The other options provided do not fit the definition of a compound sentence as they consist of only one clause or do not connect two independent thoughts.