The nature of the valves in the heart is:

Which of the following statements regarding cardiac output is incorrect?

Which structure acts as the pacemaker of the heart?

In higher vertebrates,$SA-$node helps in

What is the normal heart rate in a two-month-old infant?

Given below are two statements.
Statement $I$ - The heart sound $Dub$ is heard during ventricular diastole.
Statement $II$ - The heart sound $Lubb$ is heard during atrial systole.
In the light of above statements,select the correct option given below: