How Would Neuroscientists Explain the Early Adulthood Shifts in Behavior

How would neuroscientists explain the early adulthood shifts in behavior that are often seen in the early twenties?​

A) ​There is a decrease in cortical activity in the diencephalon-the hypothalamus and thalamus-which in turn leads to a stabilizing of endocrine activities.
B) ​There is a thickening of the corpus callosum, so information can travel more readily across the cerebral hemispheres.
C) ​There is further development in the prefrontal cortex, which is involved in higher level thinking processes.
D) ​There is increased myelination in the structures of the hindbrain-the pons, medulla, and cerebellum-which leads to greater control of impulsive behaviors.