During her morning walk, Vicki has encountered a strange dog and fear has enveloped her. Just then the dog's owner appears, pets his dog, and introduces himself and his dog to Vicki. The dog begins to wag its tail, and Vicki even pets the dog as she breathes a sigh of relief. As she begins the rest of her walk, Vicki's heart rate begins to slow down and her formerly sweaty palms are now dry. Her

calmer demeanor is due to the __________nervous system.

a. somatic
b. central
c. sympathetic
d. parasympathetic

D