A Patient Who Is 20 Weeks' Pregnant Tells the Nurse

A patient who is 20 weeks' pregnant tells the nurse that she feels more shortness of breath as her pregnancy progresses.The nurse recognizes that which of the following is true?

A) High levels of estrogen cause shortness of breath.
B) Feelings of shortness of breath are abnormal during pregnancy.
C) The hormones of pregnancy cause an increased respiratory effort.
D) She should get more exercise in an attempt to increase her respiratory reserve.