<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 30-year-old woman presents to the emergency department with breathlessness for the last hour. She is unable to provide any history due to her dyspnea. Her vitals include: respiratory rate 20min, pulse 100min, and blood pressure 14484 mm Hg. On physical examination, she is visibly obese, and her breathing is labored. There are decreased breath sounds and hyperresonance to percussion across all lung fields bilaterally. An arterial blood gas is drawn, and the patient is placed on inhaled oxygen. Laboratory findings reveal:pH 7.34pO2 63 mm HgpCO2 50 mm HgHCO3 22 mEqLHer alveolar partial pressure of oxygen is 70 mm Hg. Which of the following is the most likely etiology of this patients symptoms?? A: Impaired gas diffusion, B: Alveolar hypoventilation, C: Right to left shunt, D: Ventilationperfusion mismatch, E: Ventricular septal defect,  <response>: Based on the information provided in the question stem, the patient is a 30-year-old obese woman presenting with acute onset breathlessness and labored breathing. Physical exam reveals decreased breath sounds bilaterally suggesting a pulmonary process. Arterial blood gas shows respiratory acidosis pH 7.34, pCO2 50 mmHg. The A-a gradient Alveolar pO2 - Arterial pO2 is calculated to be 70 - 63 7 mmHg, which is normal. This rules out impaired diffusion. The elevated pCO2 indicates alveolar hypoventilation. Right to left shunt and ventricular septal defect can be ruled out based on normal A-a gradient. Ventilationperfusion mismatch remains a possibility but alveolar hypoventilation best explains the acute presentation in this patient.B: Alveolar hypoventilation 