<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:An 81-year-old man comes to the emergency department because of left-sided visual loss that started 1 hour ago. He describes initially seeing jagged edges, which was followed by abrupt, complete loss of central vision in the left eye. He has hypertension and type 2 diabetes mellitus. Blood pressure is 14589 mm Hg. Neurologic examination shows no abnormalities. A photograph of the fundoscopic findings is shown. Which of the following tests is most likely to confirm this patients underlying condition?? A: Glycated hemoglobin concentration, B: Carotid artery duplex ultrasonography, C: Erythrocyte sedimentation rate, D: CD4 T-cell count, E: Optic tonometer,  <response>: This is a clinical vignette describing a patient with acute, painless vision loss in one eye. The description of jagged edges followed by complete central vision loss is classic for retinal artery occlusion. The fundoscopic image shows a cherry red spot, which is pathognomonic for central retinal artery occlusion. This condition is often caused by an embolus, so tests should be aimed at identifying the source of embolism. Glycated hemoglobin, ESR, and CD4 count are not relevant. Optic tonometry measures intraocular pressure, which is unrelated. Carotid duplex ultrasonography is the best test to evaluate for carotid artery disease, which is a frequent source of retinal artery emboli.B: Carotid artery duplex ultrasonography 