A female cat in heat urinates more often and in many places. Male cats congregate near the urine deposits and fight with each other. Which of the following would be an ultimate cause of the male cats' response to the female's urinating behavior?

A) The males have learned to recognize the specific odor of the urine of a female in heat.
B) When the males smelled the odor, various neurons in their brains were stimulated.
C) Responding to the odor means locating reproductively receptive females.
D) Male cats' hormones are triggered by the odor released by the female.
E) The odor serves as a releaser for the instinctive behavior of the males.