**Core Concept**
The management of preterm labor involves the use of various pharmacological agents to suppress uterine contractions and delay fetal maturation. Adrenergic drugs, specifically beta-2 agonists, are often used due to their ability to selectively relax uterine smooth muscle.

**Why the Correct Answer is Right**
Ritodrine, a non-selective beta-2 agonist, works by stimulating beta-2 adrenergic receptors in the uterus, leading to relaxation of the uterine smooth muscle and a decrease in uterine contractions. This results in a delay in fetal maturation and a decrease in the risk of preterm birth. The mechanism of action involves the activation of adenylate cyclase, leading to an increase in cyclic AMP (cAMP) levels, which in turn causes relaxation of the uterine smooth muscle.

**Why Each Wrong Option is Incorrect**
* **Option A:** Terbutaline is a selective beta-2 agonist, but it is not typically used for arresting labor due to its shorter duration of action and higher risk of side effects.
* **Option B:** Metoprolol is a beta-1 selective blocker, which would actually worsen uterine contractions and is contraindicated in preterm labor.
* **Option D:** Propranolol is a non-selective beta-blocker, which would also worsen uterine contractions and is contraindicated in preterm labor.

**Clinical Pearl / High-Yield Fact**
Beta-2 agonists are a class of adrenergic drugs that are often used in the management of preterm labor, but they can have significant side effects, including pulmonary edema and cardiac arrhythmias.

**Correct Answer: C. Ritodrine**