Correct Answer: A

Rationale: Croup is the correct answer. Croup is characterized by a 'seal-like' barking cough due to inflammation and narrowing of the upper airways, particularly the larynx and trachea. It is most common in young children and can cause significant respiratory distress, especially at night. Treatment often includes humidified air and corticosteroids. Asthma (choice B) typically presents with wheezing and shortness of breath, not a barking cough. Bronchitis (choice C) is characterized by productive cough with mucus, not a barking cough. Pneumonia (choice D) often presents with fever, productive cough, and chest pain, not a barking cough.

Correct Answer: B

Rationale: The correct answer is B: Wheezing. Wheezing is a key distinguishing feature of bronchiolitis in infants, typically caused by respiratory syncytial virus (RSV) infection. Bronchiolitis is characterized by inflammation and mucus buildup in the small airways of the lungs, leading to wheezing sounds during breathing. Choices A, C, and D are incorrect because dry cough, stridor, and productive cough are not typical features of bronchiolitis in infants.

Correct Answer: C

Rationale: Absent breath sounds on the affected side are a primary symptom of congenital diaphragmatic hernia. Cyanosis, bradycardia, and tachypnea may also be present but are not the primary symptom. Cyanosis is a bluish discoloration of the skin due to poor oxygenation, bradycardia is a slower than normal heart rate, and tachypnea is rapid breathing.

Correct Answer: C

Rationale: The correct answer is to administer epinephrine. Administering epinephrine is the crucial first step in managing anaphylaxis as it helps reverse the severe allergic reaction by constricting blood vessels and relaxing airway muscles, preventing a life-threatening situation. Antihistamines (Choice A) are not the first-line treatment for anaphylaxis and should not delay the administration of epinephrine. Establishing IV access (Choice B) may be necessary but is not the initial step in managing anaphylaxis. Monitoring vital signs (Choice D) is important but should not take precedence over administering epinephrine in the acute management of anaphylaxis.

Correct Answer: C

Rationale: The correct answer is C, Respiratory syncytial virus (RSV). RSV is the leading cause of bronchiolitis, a common respiratory condition in infants that results in inflammation of the small airways in the lung. It is highly contagious and can cause severe respiratory distress in young children, particularly those under 2 years old. Choice A, Adenovirus, is not the most common cause of bronchiolitis in infants. Choice B, Influenza virus, may cause respiratory infections but is not the primary cause of bronchiolitis. Choice D, Parainfluenza virus, can cause croup and other upper respiratory infections but is not the main cause of bronchiolitis in infants.