Spontaneous depolarization of the nodal tissue in the sa node occurs at action potentials per minute:

It is 70-80 action potentials per minute.  The rate of phase 4 depolarization in the SA node sets the Heart rate, The SA node serves as the Pacemaker It has the greatest  automaticity And ability to  spontaneously generate an action potential.  

answer; i believe the correct answer is (a)0

i am positive it is c. condensing but i may be wrong