Which Time Period in a Child's Life Is Considered to Be

Which time period in a child's life is considered to be a very important time in terms of experience and neural development?

A) Before birth, during the initial time of the brain formation.
B) The first three years of life when connections are forming between neurons.
C) Once a child begins formal education, approximately at the age of 5.
D) Once a child begins puberty and the final growth in brain development begins.