The graph that best represents Lora's heart rate in the first minute is Graph D.
When Lora gets on the treadmill and starts running, the rate of her heartbeat will increase sharply. In other words, the heart rate does not start from zero as in graph (B).
This initial increase in heart rate is a normal physiological response to physical activity and is part of the body's effort to meet the increased demand for oxygen and nutrients by the working muscles.
Graph A shows a fall in the heart rate from a higher position while graph C shows a leveled heart rate.
Thus, only graph D shows what is likely to happen to Lora's heart rate in the first minute.