A. Incorrect response: See explanation B.
B. Correct response: Nitric oxide (NO) is a selective endogenous pulmonary vasodilator. When administered therapeutically, NO still functions as a selective pulmonary vasodilator for the treatment of pulmonary hypertension. The description, selective pulmonary vasodilator, means that NO reduces pulmonary vascular resistance without affecting systemic vascular resistance. At the same time, that description also means that pulmonary vascular resistance decreases only near ventilated alveoli. The results of inhaled NO are a decrease in intrapulmonary shunting and improved oxygenation. NO does not produce systemic vasodilatation because it rapidly binds to hemoglobin.
C. Incorrect response: See explanation B.
D. Incorrect response: See explanation B.