Read the following statements $\left(\mathrm{A}-\mathrm{D.}\right)$

$\left(\mathrm{A}\right)$ QRS complex in ECG indicates ventricular depolarization.

$\left(\mathrm{B}\right)$ The electrocardiograph machine is used to obtain Electrocardiogram (ECG) on graph paper.

$\left(\mathrm{C}\right)$ During a cardiac cycle, the left ventricle pumps out about 70 ml of oxygenated blood which is called the cardiac output.

$\left(\mathrm{D}\right)$ The second heart sound is associated with the closure of the semilunar valves.

How many statements from the above is/are incorrect?