Fertility in the U

Fertility in the U.S.declined in the last 100 years primarily because

A) real income has increased and children are inferior goods.
B) the tax benefits for families with children have expanded.
C) the cost of having children has decreased, primarily in terms of healthcare and education costs.
D) the cost of having children has increased, primarily in terms of the opportunity cost of the mother's foregone wages.
E) economic growth has slowed, prohibiting households from efficiently having large families.