Which of the following sentences is correct?
$I$. $ECG$ is of a great clinical significance.
$II$. Electrocardiograph is the machine used to obtain an electrocardiogram.
$III$. To obtain a standard $ECG$,a patient is connected to the machine with $3$ electrical leads (one to each wrist and to the left ankle).
$IV$. Normal activities of the heart are regulated intrinsically (auto-regulated by nodal tissue).
$V$. Electrocardiogram is the graphical representation of the electrical activity of the heart during a cardiac cycle.
Which of the following options contains all the correct statements?

• A
  $I, II, III$ and $IV$
• B
  $I, II, III, IV$ and $V$
• C
  $II, III, IV$ and $V$
• D
  $I, III, IV$ and $V$