Final answer:
The example of a compound sentence is option d) "He ran fast, and I followed slowly.", because it contains two independent clauses joined by a coordinating conjunction.
Step-by-step explanation:
The correct answer to the question "Which of the following is an example of a compound sentence?" is option d) "He ran fast, and I followed slowly." A compound sentence contains two or more main clauses that are equally important to the sentence. These clauses are typically joined by a coordinating conjunction. In the example provided, the two independent clauses ('He ran fast' and 'I followed slowly') are joined by the coordinating conjunction 'and' to form a compound sentence.