## **Core Concept**
The question tests the understanding of respiratory distress in infants, specifically the differential diagnosis of bilateral wheezing and lung hyperinflation. The clinical presentation suggests an obstructive lung disease. Key considerations include bronchiolitis, asthma, pneumonia, and foreign body aspiration.

## **Why the Correct Answer is Right**
The correct answer, **Bronchiolitis**, is a common cause of respiratory distress in infants. It is characterized by inflammation and congestion of the small airways (bronchioles) of the lung. The symptoms and signs, such as bilateral wheezing, difficulty breathing, and bilateral hyperinflation on chest X-ray (CXR) in an afebrile child with a normal white blood cell (WBC) count, are consistent with bronchiolitis. This condition is often caused by viral infections, most commonly the Respiratory Syncytial Virus (RSV).

## **Why Each Wrong Option is Incorrect**
- **Option A: Bronchial Asthma** - While asthma can present with bilateral wheezing and hyperinflation on CXR, it is less common in infants and typically associated with a personal or family history of atopy or allergic diseases.
- **Option B: Pneumonia** - Pneumonia would typically present with fever and an elevated WBC count, which is not the case here. Although pneumonia can cause difficulty breathing, the bilateral hyperinflation without consolidation on CXR makes it less likely.
- **Option D: Foreign Body Aspiration** - This condition usually presents acutely with a history of choking and unilateral symptoms (wheezing or decreased breath sounds), not bilateral symptoms as described.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that bronchiolitis is a clinical diagnosis, primarily affecting infants under 2 years of age. The diagnosis is based on history and physical examination, with CXR used to rule out other conditions. Management often focuses on supportive care, as the disease is usually viral.

## **Correct Answer: C. Bronchiolitis**