<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 21-year-old woman is evaluated for dry cough, shortness of breath, and chest tightness which occur episodically 12 times per week. She notes that she develops significant shortness of breath when running, especially during cool weather. She also says she has 1 episode of coughing attacks during the night per month. She denies any history of tobacco use. Medical history is significant for atopic dermatitis as a child, although she now rarely experiences skin flares. Family history is non-contributory. Vital signs include a temperature of 37.0C 98.6F, blood pressure of 11575 mm Hg, and heart rate of 88min. Her pulse oximetry is 98 on room air. Physical examination reveals normal air entry and no wheezes. A chest X-ray is normal. Spirometry findings are within normal parameters. Which of the following is the best next step in the management of this patients condition?? A: Sweat chloride test, B: Methacholine challenge test, C: Skin-prick testing, D: Ciliary studies, E: Clinical observation without further evaluation,  <response>: This is a clinical case scenario about a 21-year-old woman with episodic dry cough, shortness of breath, and chest tightness, suggestive of asthma. The key findings are episodic symptoms triggered by exercise and cold weather, nighttime cough, history of atopic dermatitis, and normal physical exam, chest X-ray and spirometry. The choices provided are diagnostic tests for different conditions:A Sweat chloride test - evaluates for cystic fibrosisB Methacholine challenge test - evaluates for bronchial hyperresponsiveness as seen in asthmaC Skin prick testing - evaluates for allergic triggersD Ciliary studies - evaluates for primary ciliary dyskinesia E Clinical observation - no further testingBased on the clinical presentation, the methacholine challenge test is the best next step to confirm the diagnosis of asthma. The history and normal initial workup is consistent with exercise-induced bronchospasm, a variant of asthma. The methacholine challenge can help establish the diagnosis by demonstrating bronchial hyperresponsiveness.B: Methacholine challenge test 