Concept:The organ that separates an animal’s body from the outside environment is the outer protective covering.
Explanation:The skin is the largest organ in an animal’s body and covers the entire body surface.
It acts as a barrier against pathogens, chemicals, water loss, and physical injury.
It is the first line of defense of the body.
The urinary bladder, stomach, and lung are internal organs.
They do not form the outer barrier between an animal and its external environment.
Therefore, the correct organ is the skin.
Answer:D. Skin