<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 13-year-old boy is brought to the physician because of a 4-month history of worsening dizziness, nausea, and feeling clumsy. An MRI of the brain shows a well-demarcated, 4-cm cystic mass in the posterior fossa. The patient undergoes complete surgical resection of the mass. Pathologic examination of the surgical specimen shows parallel bundles of cells with eosinophilic, corkscrew-like processes. Which of the following is the most likely diagnosis?? A: Medulloblastoma, B: Ependymoma, C: Pilocytic astrocytoma, D: Craniopharyngioma, E: Pinealoma,  <response>: This is a clinical case about a 13-year-old boy with symptoms of dizziness, nausea, and clumsiness that have been worsening over 4 months. An MRI shows a cystic mass in the posterior fossa back part of the brain. After surgical resection, pathology shows parallel bundles of cells with corkscrew-like processes, which provides a key clue. Based on the location of the mass in the posterior fossa and the pathology findings, this narrows the differential diagnosis. The corkscrew-like processes indicate the tumor cells are likely astrocytes. Of the choices given, pilocytic astrocytoma would be the most likely diagnosis.Medulloblastoma and ependymoma are less likely as they do not show the corkscrew processes. Craniopharyngioma and pinealoma would not be found in the posterior fossa location.C: Pilocytic astrocytoma 