The sends out an electrical impulse that regulates the heartbeat.

The SA node

Answer choices are:

A.      The AV node

B.      The SA node

C.      The purkinje fibers

D.     The AV bundle

The SA node is the heart's natural pacemaker consisting of a cluster of cells located in the upper part of the wall of the right atrium. (the right upper chamber of the heart). The electrical impulses are produced and sent out from there to regulate heartbeat. This is also called the sinus code.  

The SA nodes sends out electrical impulses that regulates the heartbeat. The SA also called the sinus node generates the electrical signals which moves from cell to cell down through the heart until it reaches the atrioventricular node, a cluster of cells situated in the center of the heart between the atria and ventricles. In other words, SA nodes controls the heart rate by generating electrical impulses and then sending signals through the heart muscle, causing the heart to contract and pump blood throughout the body.

Some of her  assignments would be creation of drugs. she is a medical chemist after all so she'd need to have the necessary knowledge to make medicine which can later be sold in a pharmacy 

The category is the thing that is most simmilar throughout a period