Which sentence represents a correct example of a run-on sentence?

The sentence that accurately exemplifies a run-on sentence is found in the option that begins with "Running is fun it can also be tiring."

A run-on sentence occurs when two or more independent clauses are joined without appropriate punctuation or conjunctions. In this instance, "Running is fun" and "it can also be tiring" are both complete thoughts that could stand alone as separate sentences. However, they are improperly connected without a coordinating conjunction or punctuation to clarify their relationship.

To correct this run-on, one might use a semicolon, a conjunction, or separate them into two distinct sentences, such as, "Running is fun; it can also be tiring" or "Running is fun. It can also be tiring." This illustrates the essential idea that independent clauses require proper linkage to avoid confusion and maintain clarity in writing.