N a study of physical endurance, researchers observed significant increases in the heart rates and breathing rates of participants immediately after they engaged in strenuous exercise. Which statement best explains the increase in the heart rate and the breathing rate during exercise?

The water concentration in the blood increases.
The water concentration in the blood increases.

Body cells require increased oxygen as energy is expended.
Body cells require increased oxygen as energy is expended.

Muscle cells increase in temperature and require fluid to reduce the temperature.
Muscle cells increase in temperature and require fluid to reduce the temperature.

An increase in muscle activity causes increases in glucose levels in red blood cells.