Q. A 7-year-old boy is brought to the pediatrician by his mother due to recurrent episodes of coughing, wheezing, and difficulty breathing, especially during the night and after exercise. His mother also reports that the boy's father has a history of hay fever and eczema. The child's vital signs are as follows: temperature 36.8°C (98.2°F), heart rate 90 beats/min, respiratory rate 22 breaths/min, and blood pressure 105/65 mm Hg. On physical examination, the boy has expiratory wheezing and mild use of accessory muscles for breathing. Which of the following is the most likely diagnosis?