Answer: A. smooth
Explanation:
Any muscle that works voluntarily is a skeletel system. and cardiac muscles are things like the heart and lungs. I hope this helps!
John Snow, Henry Whitehead, the Broad Street pump,
The right answer is Electrocardiography (or Electrocardiogram).
In a typical plot, one can notice five characteristic waves. They are called P, Q, R, S and T. The illustration below shows what a normal electrocardiogram looks like:
* the P wave marks the depolarization during the contraction of the atria;
* the PR interval indicates the time required to transmit the electrical impulse of the sinus node of the atria to the ventricular muscles;
* the QRS complex marks depolarization and ventricular contraction;
* the QT interval corresponds to the global ventricular repolarization;
* T wave refers to the end of ventricular repolarization.
