Explain what selective permeability is and how this relates to the cell membrane? pls help

Which of the following statements about brain development and early childhood is true? the brain of a 5 year old is 60 percent the size of an adult brain the overall size of the brain does not increase dramatically from ages 3-15 by the time a child is 3 years of age, the brain is 25 percent of it's adult size the development that occurs inside the brain ends at the onset of adolescence