<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 2-year-old boy is brought to the physician for a well-child examination. Since infancy, he has frequently had large-volume stools that are loose and greasy. He was treated for otitis media twice in the past year. He has a history of recurrent respiratory tract infections since birth. He is at the 5th percentile for height and 3rd percentile for weight. Vital signs are within normal limits. Examination shows softening of the occipital and parietal bones. Scattered expiratory wheezing and rhonchi are heard throughout both lung fields. Which of the following is the most likely cause of this patients symptoms?? A: Deficient α1 antitrypsin, B: Gliadin autoantibodies, C: CFTR gene mutation, D: Absent T cells, E: Impaired ciliary function,  <response>: This is a clinical vignette describing a 2-year-old boy with chronic diarrhea, failure to thrive, recurrent infections, and bony abnormalities. The key findings are greasy stools, short stature, softening of occipital and parietal bones, and recurrent respiratory infections. This constellation of findings is classic for cystic fibrosis. Choice C, CFTR gene mutation, is therefore the most likely diagnosis.Choices A, B, D, and E can all cause some of the symptoms described, but do not explain the full clinical picture. Deficient α1 antitrypsin A causes lung disease but not the GI or skeletal findings. Gliadin autoantibodies B could cause the diarrhea but not the other problems. Absent T cells D would lead to severe immunodeficiency. Impaired ciliary function E could explain the recurrent respiratory infections but not the other findings.C: CFTR gene mutation 