Default network
When the brain is unoccupied, an fMRI indicates that blood continues to flow via a web of brain regions called the default network.
The default network is a web of brain regions that have activity that corresponds greatly with each other and different from other networks within the brain. The default network is active when an individual's attention is not concentrated on the external environment and it is measured with the functional magnetic resonance imaging technique (fMRI).
Hydrogen because it only has one valence electron I believe.
Answer:
2 because the central nervous system includes the brain, cerebellum, cerebrum, brain stem, etc.
Cladistics is based on the shared characteristics between organisms and their network of evolutionary relationships