Exercise enhances the efficiency of which two systems in the body?

The correct option highlights the improvement in the circulatory and respiratory systems due to exercise. Engaging in regular physical activity enhances the heart's ability to pump blood more efficiently, which increases the oxygen delivery to muscles and other tissues. This efficiency allows for better utilization of oxygen during exercise, contributing to improved endurance and overall cardiovascular health.

Additionally, exercise stimulates the respiratory system by strengthening the muscles involved in breathing, such as the diaphragm and intercostal muscles. This leads to increased lung capacity and improved oxygen intake, which further supports aerobic performance and the body’s ability to sustain prolonged physical activity.

In contrast, while the digestive system plays a role in nutrient absorption and energy provision, it is not as directly enhanced by exercise in the same manner as the circulatory and respiratory systems. Similarly, improvements in the nervous and endocrine systems are important but are secondary to the immediate changes that exercise creates in oxygen transport and consumption. Lastly, although the skeletal and muscular systems benefit from exercise in terms of strength and flexibility, the key focus here is on the systems that primarily facilitate oxygen delivery and energy production during physical activity.