The graph shown displays a market with an externality. 
Which of the following statements is true?This shows a negative consumption externality.The efficient quantity is 7 units.The size of the externality is $12 per unit.
Definitions:
Oligodendrocytes
Glial cells in the central nervous system that produce myelin, a substance that insulates nerve fibers to increase the speed at which impulses are conducted.
CNS Cavities
Hollow spaces within the central nervous system, including ventricles in the brain, filled with cerebrospinal fluid.
Astrocytes
Astrocytes are star-shaped glial cells in the brain and spinal cord involved in providing support and nutrition to nerve cells, maintaining the blood-brain barrier, and repairing the brain and spinal cord following traumatic injuries.
Microglia
Specialized immune cells found in the brain and spinal cord, involved in the maintenance of nerve cells and the response to injury or disease.
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