Tammy is using a treadmill, and when she puts her hands on the bar, sensors read her heart rate. Today, the sensors are telling Tammy that she is reaching 183, which is the highest rate in her target zone. What should she do to get the most effective workout? A. Increase her running speed without adjusting the incline. B. Use the machine to maintain or decrease her intensity. C. Do additional aerobic exercises immediately after the treadmill. D. Use the machine to increase the incline and intensity.