With Regard to the Structure and Function of the Placenta,the

With regard to the structure and function of the placenta,the maternity nurse should be aware that:

A) As the placenta widens,it gradually thins to allow easier passage of air and nutrients
B) As one of its early functions,the placenta acts as an endocrine gland
C) The placenta is able to keep out most potentially toxic substances,such as cigarette smoke,to which the mother is exposed
D) Optimal blood circulation is achieved through the placenta when the woman is lying on her back or standing