Respiratory system, because the lungs and diaphragm would get the oxygen from the air, and transfer them to the circulatory system (that's a pretty basic explanation, there's much more to it)
Answer:
The nervous system is stimulated from the environment, through sensory receptors. A stimulus is any form of energy that can be detected by the body. ... Animals normally only respond to stimuli which they select; they filter out certain stimuli that surround them, and react to others they choose to accept.
They are all freshwater. So the closest would be c. an estuary since it has a free connection with the sea since the sea is not freshwater.
So C.
hope this helps!
D: Surface-water runoff from rain
