Which of the following is true of the structures of the electrical conduction system?

A) The AV valve is the pacemaker.
B) In normal sinus rhythm, the electrical signal arises within the SA node.
C) The His-Purkinje system spreads the electrical system from the right atrium to the left atrium.
D) The purpose of the AV node is to increase the speed at which the cardiac impulse moves from the atria to the ventricles.