most likely to be A which is probably an artery which carries blood away from the heart Nd tens to carry oxygen rich blood
the leg doesnt contain aveoli this is found in the lungs so its not B
since its oxygen rich little carbon dioxide will be present in this structure so its not C
this part cant be part of the respiratory system as the respiratory system includes lungs, mouth and etc but not the legs so it cant be D
hope that helps
