In all the leads of $ECG$,all following are positive waves except

What are the systolic and diastolic blood pressures of a healthy adult human?

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?

Draw a standard $ECG$ and explain the different segments in it.

In the following diagrammatic representation of a standard $ECG$,the '$T$' wave represents:

Which of the following statements regarding blood pressure is correct?