Assertion : The cardiac output of an ordinary man and of an athlete is the same
Reason : It is impossible to alter the stroke volume as well as heart rate.

Answer: DSolution: The stroke volume multiplied by the heart rate (no. of beats per min.) gives the cardiac output. Therefore, the cardiac output can be defined as the volume of blood pumped out by each ventricle per minute and average $5000$ mL or $5$ litres in a healthy individual. The body has the ability to alter the stroke volume as well as the heart rate and thereby the cardiac output. For example, the cardiac output of an athelete will be much higher than that of an ordinary man.