<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 7-year-old Caucasian girl with asthma presents to her pediatrician with recurrent sinusitis. The patients mother states that her asthma seems to be getting worse and notes that lung problems run in the family. The patient has had 2 episodes of pneumonia in the last year and continues to frequently have a cough. Her mother says that 1 of her nieces was recently diagnosed with cystic fibrosis. On physical examination, the child has clubbing of the nail beds on both hands. A chloride sweat test is performed on the patient, and the childs sweat chloride concentration is found to be within normal limits. The physician is still suspicious for cystic fibrosis and believes the prior asthma diagnosis is incorrect. Which of the following diagnostic tests would aid in confirming this physicians suspicions?? A: A chest radiograph, B: A nasal transepithelial potential difference, C: A complete blood count, D: A chest CT scan, E: A urinalysis,  <response>: This is a clinical case scenario about a 7-year-old girl with a history of asthma and recurrent sinusitis whose mother is concerned her symptoms may indicate cystic fibrosis. The key findings in the stem are a family history of lung problems, 2 episodes of pneumonia in the past year, persistent cough, clubbing of the nail beds, and a normal sweat chloride test. The question asks which diagnostic test would help confirm the physicians suspicion of cystic fibrosis despite the normal sweat chloride test. Choices include a chest X-ray, nasal transepithelial potential difference measurement, complete blood count, chest CT, and urinalysis. A nasal transepithelial potential difference test can help diagnose cystic fibrosis in cases where sweat chloride testing is inconclusive. This measures electrical potential difference across the nasal epithelium, which is abnormally more negative in CF patients due to defective chloride transport. The other tests may show secondary findings but would not directly evaluate CFTR function.B: A nasal transepithelial potential difference 