Animal communication refers to the release of one or more stimulus signals by individuals, which causes the receiving individuals to react. The signal itself is meaningless, but it can be recognized quickly. More importantly, it represents a series of complex biological attributes, such as gender, age, body shape, hostility or friendliness. Animals communicate information through actions, sounds, smells and secretions (sex pheromones). Therefore, actions, sounds, smells and secretions (sex pheromones) can be identified quickly.
So choose: D.