Psychologists study animals because

A) animal behavior is just as complex as human behavior.
B) experiments on people are generally considered to be unethical.
C) the ethical treatment of animals is not mandated by professional guidelines.
D) similar processes often underlie animal and human behavior.

Psychologists study animals because similar processes often underlie animal and human behavior. While animal behavior is not as complex as human behavior, studying animals can provide valuable insights into the underlying mechanisms of behavior, learning, and motivation that are also present in humans. Additionally, animal studies can be used to explore questions that are considered unethical to examine in humans, such as the effects of certain drugs or brain lesions on behavior. However, it is important to note that professional guidelines do mandate the ethical treatment of animals in psychological research.