<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 65-year-old woman presents to her physician with chronic breathlessness. Her condition has been progressively worsening over the last 20 years despite treatment with inhaled salbutamol, inhaled corticosteroids, and multiple courses of antibiotics. She has a 30-pack-year smoking history but quit 20 years ago. Her pulse is 104min and respirations are 28min. Physical examination shows generalized wasting. Chest auscultation reveals expiratory wheezes bilaterally and distant heart sounds. Pulmonary function testing shows a non-reversible obstructive pattern. Her carbon monoxide diffusion capacity of the lungs DLCO is markedly reduced. Which of the following explains the underlying mechanism of her condition?? A: Accumulation of fluid in the alveolar space, B: Contraction of pulmonary smooth muscles, C: Decreased partial pressure of alveolar oxygen, D: Diminished surface area for gas exchange, E: Inflammation of the pulmonary bronchi,  <response>: Based on the information provided in the question stem, this patient has a long history of progressive breathlessness and obstructive lung disease despite treatment. Key findings include a 30 pack-year smoking history, tachypnea, wheezing on exam, irreversible obstructive pattern on PFTs, and a reduced DLCO. The reduced DLCO along with her smoking history points towards an underlying emphysematous process reducing gas exchange surface area in the lungs. Choice D Diminished surface area for gas exchange matches this assessment.Choices A, B, C, and E can all cause breathlessness but do not fit with the irreversible obstructive disease and reduced DLCO described here.D: Diminished surface area for gas exchange 