Where does the circulation of oxygenated (pure) blood occur in humans?

• A
  From the left atrium to the left ventricle during atrial systole.
• B
  From the right atrium to the right ventricle during ventricular systole.
• C
  From the right ventricle to the aorta during ventricular systole.
• D
  From the pulmonary vein to the left atrium during atrial systole.