**Core Concept**
Fetal lung maturity is crucial for safe vaginal delivery. The primary indicator of fetal lung maturity is the presence of phospholipids, particularly lecithin and sphingomyelin. A deficiency of these phospholipids can lead to respiratory distress syndrome (RDS) in newborns.

**Why the Correct Answer is Right**
The correct answer is **Betamethasone**. It is administered to the mother to accelerate fetal lung maturation. Betamethasone stimulates the production of surfactant, a critical component of fetal lung fluid that reduces surface tension and prevents alveolar collapse. This results in improved lung compliance and gas exchange. The mechanism involves the activation of glucocorticoid receptors, which upregulate the expression of surfactant protein genes.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not directly induce fetal lung maturity. Instead, it is used for other indications, such as asthma and COPD.
**Option B:** This option is incorrect because it is used for other purposes, like treating hypertension and heart failure.
**Option C:** This option is incorrect because it does not have a role in fetal lung maturation.

**Clinical Pearl / High-Yield Fact**
The administration of corticosteroids like betamethasone to pregnant women at risk of preterm delivery can significantly reduce the incidence of RDS in newborns. This is a critical aspect of perinatal medicine, and clinicians should be aware of the benefits and indications for corticosteroid therapy.

**Correct Answer: C. Betamethasone**