A 16-month-old boy and his adoptive parents present to your office with a complaint of cough and concern about the patient's weight. The parents indicate that they don't have much information about the patient's birth parents and since adopting him four months ago they have noticed daily shortness of breath, cough and wheezing. He is also a fussy eater and is in the second percentile of weight on the growth chart. Which lab finding is most consistent with the diagnosis? A. elevated exhaled nitric oxide testing B. elevated sweat chloride C. elevated white blood cell count D. positive skin allergy test