47. 大腸癌發生的過程一般需經歷了兩個階段：腺瘤(adenoma)的形成，稱為腫瘤起始(tumor initiation)，以及腺瘤進展為大腸癌，稱為腫瘤進展(tumor progression)。哪些基因改變被認為是腫瘤起始(tumor initiation)而不是腫瘤進展(tumor progression)的重要步驟？(1) Loss of adenomatous polyposis coli(APC)gene function(2) Loss of function of DCC(deleted in colon cancer)genes(3) Mutations in DNA mismatch repair(MMR)genes(4) Allelic deletion of chromosome 17p at the locus that contains the TP53 gene(5) K-ras gene mutations(A) (1)(B) (1)＋(2)(C) (1)＋(2)＋(3)(D) (1)＋(2)＋(3)＋(4)(E) (1)＋(2)＋(3)＋(4)＋(5)