Which of the following indicates a normal sinus rhythm?

A normal sinus rhythm is characterized by a heart rate that falls within a specific range, which is between 60 and 100 beats per minute (bpm). This range reflects the typical functioning of the heart when it is properly responding to the body's demands for oxygen and nutrients. A heart rate within this range also implies that the electrical signals responsible for triggering heartbeats are originating from the sinoatrial node, maintaining a consistent and coordinated rhythm.

In addition to the appropriate rate, a normal sinus rhythm is typically regular and follows a specific pattern, which includes consistent P waves preceding each QRS complex on an ECG. However, the defining feature that directly indicates normal sinus rhythm in this question is the heart rate within the range of 60-100 bpm. This distinguishes normal sinus rhythm from other irregular rhythms or abnormal heart conditions, which often exhibit rates outside this normal range.