<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 40-year-old man presents with an episode of rectal bleeding. He is concerned because his mother died of colorectal cancer at 50 years of age. He has no further information about his family history. Physical examination and digital rectal examination are normal. He undergoes a colonoscopy and is found to have innumerable adenomas in the left side of the colon ranging in size from 415 mm. Which of the following is the most likely underlying mechanism of this patient illness?? A: Mutation in DNA mismatch repair genes, B: Alterations in STK11 gene, C: Mutations of the APC gene, D: Inactivation of RB1 gene, E: Inactivation of BRCA1 and BRCA2 genes,  <response>: This is a clinical vignette describing a 40-year-old man with rectal bleeding and a family history of early-onset colorectal cancer in his mother. He is found to have numerous adenomatous polyps in the left colon on colonoscopy. The question asks about the most likely underlying genetic mechanism for his condition. Based on the clinical presentation of numerous colorectal adenomas at a young age, the most likely diagnosis is familial adenomatous polyposis FAP. FAP is caused by germline mutations in the APC tumor suppressor gene. Patients with FAP develop hundreds to thousands of colorectal adenomas beginning in their teens or twenties. Without treatment, colorectal cancer inevitably develops. Therefore, the most likely underlying genetic mechanism in this patient is a mutation in the APC gene.C: Mutations of the APC gene 