An Experimenter Finds That a Male Chimpanzee Always Has an Increased

An experimenter finds that a male chimpanzee always has an increased heartbeat when he sees a picture of a female chimpanzee.The experimenter starts to present a buzzer just before presenting the picture of the female chimp.The experimenter repeats this procedure until the male chimp responds with an increased heartbeat to the sound of the buzzer alone.In this situation,the unconditioned response (UR) is the

A) increased heartbeat.
B) female's picture.
C) sound of the buzzer.
D) experimenter.