**Core Concept**
Bronchiolitis is a common lower respiratory tract infection primarily affecting infants and young children, characterized by inflammation and congestion of the small airways. The treatment of choice aims to alleviate symptoms, support respiratory function, and prevent complications.

**Why the Correct Answer is Right**
The treatment of choice in bronchiolitis is primarily supportive care, as the condition is usually caused by viral pathogens, such as respiratory syncytial virus (RSV), and does not respond to antibiotics. **Salbutamol** (a short-acting beta-2 agonist) can be used to relieve bronchospasm and improve lung function, but its use is limited to severe cases. **Oxygen therapy** is essential to maintain adequate oxygen saturation levels. **Humidified oxygen** is particularly effective in reducing the work of breathing and improving symptoms. **Ribavirin** is an antiviral medication that may be used in severe cases, particularly in high-risk patients, such as those with underlying heart or lung disease.

**Why Each Wrong Option is Incorrect**
**Option A:** **Corticosteroids** are not the treatment of choice in bronchiolitis, as they can actually worsen the condition by suppressing the immune system and increasing the risk of secondary bacterial infections.
**Option B:** **Antibiotics** are ineffective against viral infections and should not be used in the treatment of bronchiolitis.
**Option C:** **Methylxanthines** (such as theophylline) are not typically used in the treatment of bronchiolitis and can have significant side effects.

**Clinical Pearl / High-Yield Fact**
The use of **ribavirin** in combination with mechanical ventilation may be beneficial in severe cases of bronchiolitis, particularly in high-risk patients.

**Correct Answer:** D. Humidified oxygen