**Core Concept**
Beta agonists are a class of medications that stimulate the beta-adrenergic receptors in the body, leading to various physiological effects such as increased heart rate, bronchodilation, and uterine relaxation. In the context of pregnancy, beta agonists can be used to manage preterm labor by relaxing the uterine muscles and reducing contractions.

**Why the Correct Answer is Right**
The correct answer is **Ritodrine**, a selective beta-2 adrenergic agonist that is specifically used to inhibit uterine contractions and delay preterm labor. Ritodrine works by stimulating the beta-2 receptors in the uterus, which leads to relaxation of the uterine smooth muscle and a decrease in the frequency and intensity of contractions. This allows for a temporary delay in preterm labor, giving healthcare providers time to administer corticosteroids to promote fetal lung maturity and prepare for delivery.

**Why Each Wrong Option is Incorrect**
**Option A:** **Terbutaline** is another beta-2 agonist, but it is primarily used to treat asthma and chronic obstructive pulmonary disease (COPD), not preterm labor.
**Option B:** **Salbutamol** is also a beta-2 agonist, commonly used as a bronchodilator for asthma and COPD, but not for preterm labor.
**Option C:** **Isoproterenol** is a non-selective beta agonist that can stimulate both beta-1 and beta-2 receptors, but it is not typically used to manage preterm labor.

**Clinical Pearl / High-Yield Fact**
Beta agonists can cause maternal tachycardia, tremors, and anxiety as side effects, highlighting the need for close monitoring during treatment for preterm labor.

**Correct Answer:** C. **Isoproterenol**