The correct option is D All of these
Electrocardiograph is a machine that produces electrocardiogram. ECG is a graphical representation of the electrical activity of the heart during a cardiac cycle. The ECG produces peaks and each peak is marked with a letter from P to T (PQRST waves) that corresponds to a specific electrical activity of the heart. By counting the number of QRS complexes that occur in a given time period, the heart beat rate of an individual can be determined. Hence, ECG gives the information of PQRST waves, heart beat rate and electrical activity of the heart.