Which of the following statements is true? Most of the factors that regulate the heart rate are extrinsic factors. Chronotropic properties refer to the contractile force of the heart. The average person has about 2-3L of blood in their body. Diastole is the contraction phase of the heart cycle.

The correct answer is: The average person has about $2-3L$ of blood in their body.<br /><br />Explanation:<br />- Most of the factors that regulate the heart rate are intrinsic factors, such as the autonomic nervous system and hormones.<br />- Chronotropic properties refer to the rate of change of the force of contraction of the heart, not the contractile force itself.<br />- The average person has about $2-3L$ of blood in their body, which is a true statement.<br />- Diastole is the relaxation phase of the heart cycle, not the contraction phase.