**Core Concept**
Long-acting beta agonists (LABAs) are a class of medications used in the management of asthma and chronic obstructive pulmonary disease (COPD). They work by stimulating the beta-2 adrenergic receptors in the lungs, causing bronchodilation and improving lung function. LABAs are typically administered twice daily due to their relatively short duration of action.

**Why the Correct Answer is Right**
Indacaterol is a once-daily LABA that offers a longer duration of action compared to other LABAs like salmeterol and formoterol. This is due to its unique pharmacokinetic profile, which allows for a higher peak plasma concentration and a longer half-life. Indacaterol binds to the beta-2 adrenergic receptors with high affinity, producing sustained bronchodilation for up to 24 hours. This makes it an ideal option for patients who require once-daily medication.

**Why Each Wrong Option is Incorrect**
**Option A:** Salmeterol is a LABA with a duration of action of approximately 12 hours, requiring twice-daily administration. It is not suitable for once-daily use.
**Option B:** Formoterol is another LABA with a duration of action of around 12 hours, also requiring twice-daily administration. It is not as long-acting as indacaterol and is not suitable for once-daily use.
**Option D:** Terbutaline is a short-acting beta agonist (SABA) with a duration of action of approximately 4-6 hours, making it unsuitable for long-term use as a LABA.

**Clinical Pearl / High-Yield Fact**
When selecting a LABA, it is essential to consider the patient's specific needs and the medication's duration of action. Patients who require once-daily medication may benefit from indacaterol, while those who require twice-daily medication may be better suited to salmeterol or formoterol.

**✓ Correct Answer: C. Indacaterol**