Answer: (D)
Explanation: biotic factors depend among abiotic factors, meaning that living things need non-living things in order to survive. That also means that biotic factors everywhere including the surrounding area need to be thought of in this sense so that they are able to survive in the environment they are in.
C. The brain sends messages to the spinal cord
The hypothalamus sends signals to the pituary glands. The hypothalamus releases dopamine, so I think dopamine is a good answer?