**Core Concept**
The lung surfactant system is crucial for reducing alveolar surface tension, thereby facilitating gas exchange and preventing alveolar collapse. The surfactant is a complex mixture of phospholipids, proteins, and other components that are produced by type II pneumocytes in the alveolar lining.

**Why the Correct Answer is Right**
Surfactant is composed of approximately 90% phospholipids, with phosphatidylcholine (PC) being the most abundant species. However, surfactant also contains other minor surfactants, including phosphatidylglycerol (PG), phosphatidylinositol (PI), and others. These minor surfactants play a crucial role in stabilizing the surfactant film and modulating its surface tension. The correct answer refers to one of these minor surfactants, which is essential for maintaining optimal lung function.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not specify a known minor surfactant in the lung.
* **Option B:** This option is incorrect as it is not a recognized component of lung surfactant.
* **Option C:** This option is incorrect as it is not a known minor surfactant in the lung.

**Clinical Pearl / High-Yield Fact**
The surfactant system is critical for maintaining lung function, especially in preterm infants. Surfactant deficiency or dysfunction is a common cause of respiratory distress syndrome (RDS) in newborns. Early administration of surfactant replacement therapy can significantly improve outcomes in these patients.

**Correct Answer:** D. Phosphatidylglycerol (PG) is a minor surfactant in the lung, playing a crucial role in stabilizing the surfactant film and modulating its surface tension.