What is a role of the pacemaker or sinoatrial node (san)?
a. to initiate contraction of the ventricle
b. to pass the excitation through purkinje fibres
c. to originate excitation in myogenic muscle
d. to cause the relaxation of the atria

C. To originate the excitation in the myogenic muscle. The SA node initiates the electrical impulse that goes through the heart and causes the depolarization of the right atrea 

The return of the wolf to yellowstone national park will probably affect the bird population to some degree, not significantly. while wolves will hunt birds when necessary, they prefer to hunt larger prey. the bird population will most likely only be affected when hunting is scarce for the wolves. birds of prey will also probably not be affected as much as other birds who spend more time on the ground hunting for food as the tend to spend more time in the air or in trees since they do not need to stay on the ground for long due to the nature of the way they hunt.