**Core Concept**
The underlying principle being tested here is the clinical presentation of respiratory distress in infants, specifically the differential diagnosis of wheezing and hyperinflation of the lungs. The case highlights the importance of distinguishing between infectious and non-infectious causes of respiratory illness in young children.

**Why the Correct Answer is Right**
The clinical presentation of bilateral wheezing and hyperinflation of the lungs, coupled with a normal white blood cell count, is highly suggestive of viral-induced asthma or bronchiolitis. This condition is most commonly caused by the respiratory syncytial virus (RSV), which is a major cause of lower respiratory tract infections in infants. The absence of fever and a normal WBC count further supports this diagnosis, as these are typical findings in viral infections.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because croup, a laryngotracheobronchitis, typically presents with a barking cough, stridor, and often fever, which is not consistent with the given clinical scenario.
* **Option B:** This option is incorrect because bronchopulmonary dysplasia (BPD) is a chronic lung disease primarily affecting premature infants, often requiring mechanical ventilation and oxygen therapy, which is not indicated in this case.
* **Option C:** This option is incorrect because cystic fibrosis (CF) typically presents with chronic respiratory symptoms, such as recurrent pneumonias, and malnutrition, which is not consistent with the acute presentation of this case.

**Clinical Pearl / High-Yield Fact**
In infants with respiratory distress, it is essential to consider the possibility of viral-induced asthma or bronchiolitis, especially when wheezing and hyperinflation of the lungs are present, and to rule out other causes such as infectious diseases and chronic lung conditions.

**Correct Answer: C. Bronchiolitis**