What Did the University of Richmond Neuroscientist Craig Kinsley Mean

What did the University of Richmond neuroscientist Craig Kinsley mean when he said "mothers are made, not born"?

A) Anyone can be a good mother if she reads enough parenting books.
B) The anxiety of raising kids will eventually train a parent into being better.
C) Mothers begin to observe other parents once they have a child.
D) Hormones during pregnancy prepare the mother to care for offspring.