The more complex an animal's response to a stimulus, the more likely it is that the animal has (1 point) correct answer is: many interneurons

Your answer is correct, as confirmed. In addition, these interneurons have the main function of bridging the sensory and motor neurones to the spinal column, and brain, which comprises the central nervous system. It is considered to be one of the most abundant neurone types which our body has about 100 billion of these neurons.

Carbon dioxide is the correct answer