A child presents to the emergency department with fever and mild respiratory distress.He was started on oral antibiotics and showed initial improvement,but later deteriorated again with fever,wheeze and exaggerated breathlessness.Radiographs of chest showed hyperluscency and Pulmonary Function Tests showed an obstructive pattern.The most probable diagnosis is:

• A. Follicular Bronchitis
• B. Bronchial Asthma
• C. Bronchiolitis Obliterans
• D. Pulmonary Alveolar Proteinosis