Which of the Following Statements Are True of External Respiration

Which of the following statements are true of external respiration and internal respiration (Select all that apply) ?

A) The "P" in PO2 means "presence" of oxygen.
B) In the alveoli,PCO2 is low and PO2 is high.
C) In the tissues,PO2 is high and PCO2 is low.
D) Internal respiration takes place in the pulmonary capillaries.
E) External respiration takes place in the nasal cavities as the air is warmed.
F) The pressure gradient of a gas is much the same as a concentration gradient.