Answer:
The letter "A" represents the lungs.
Step-by-step explanation:
The lungs are spongy, elastic organs formed by millions of air-filled alveoli. The main purpose of the lungs is to provide our blood with oxygen, which is transported to the body cells. The other respiratory organs have the function of directing the air to the lungs, it is the same that occurs the conversion of venous blood (oxygen-poor and high carbon dioxide blood) into arterial blood (oxygen-rich blood).
In the image shown in the question above, the lungs are the two structures represented by the letter A.