The given figure shows a schematic plan of blood circulation in humans with labels $A$ to $D$. Identify the label and give its functions.

• A
  $C$ - Vena cava - takes blood from body parts to right auricle,$pCO_2 = 45 \ mm \ Hg$
• B
  $D$ - Dorsal aorta - takes blood from heart to body parts,$pO_2 = 95 \ mm \ Hg$
• C
  $A$ - Pulmonary vein - takes impure blood from body parts,$pO_2 = 60 \ mm \ Hg$
• D
  $B$ - Pulmonary artery - takes blood from heart to lungs,$pO_2 = 90 \ mm \ Hg$