Which one represents pulmonary circulation?
a. Left auricle (oxygenated blood) $\rightarrow$ lungs (deoxygenated blood) $\rightarrow$ Right auricle
b. Left auricle (deoxygenated blood) $\rightarrow$ lungs (oxygenated blood) $\rightarrow$ Right auricle
c. Left auricle (oxygenated blood) $\rightarrow$ lungs (deoxygenated blood) $\rightarrow$ Left auricle
d. Right auricle (deoxygenated blood) $\rightarrow$ lungs (oxygenated blood) $\rightarrow$ Left auricle

Hint: The pulmonary circulation was discovered by the physician William Harvey, it is the part of the circulatory system, generally the circulation is classified into the pulmonary and systemic circulation. Where in pulmonary circulation impure blood is carried to the lungs, in systemic circulation pure blood is carried to body parts.

Complete answer:
The pulmonary circulation in humans consists of the following aspects.
- In humans, the deoxygenated blood that is collected from the body parts is carried to the Right atrium.
- From the right atrium, the blood is pumped to the right ventricle through tricuspid valves.
- The deoxygenated blood which came to the right ventricle is pumped to the lungs through the pulmonary arteries.
- In the lungs, the blood is purified and gets oxygenated.
- The purified oxygenated blood from the lungs is now carried to the Left atrium through pulmonary veins.
- From the right atrium, oxygenated blood is pumped to the right ventricle through mitral valves.
- Finally from the right ventricle, the oxygenated blood is carried to the body parts through Aortic valves.
- This completes the one cycle of the circulation i.e., Right auricle (deoxygenated blood) $\rightarrow$ lungs (oxygenated blood) $\rightarrow$ Left auricle.

Hence, The correct answer is option (D).

Note: Significant medical conditions that affect the pulmonary circulation are Pulmonary hypertension, which means an increase in resistance to the pulmonary arteries, and any blood clot in the pulmonary circulation may cause pulmonary embolism, and cardiac shunt, etc.