The goal of this observational study is to learn about Influencing factors of intestinal microecological changes before and after colonoscopy. The main questions it aims to answer are: * \[question 1\] The process of colonoscopic gas insufflation affects the intestinal microecology. Will the use of carbon dioxide gas insufflation can reduce the changes of intestinal microecology after colonoscopy? * \[question 2\] Can the appendix act as a reservoir for microorganisms to accelerate the recovery of intestinal microecology after colonoscopy？ Participants will be asked to accept colonoscopy for once. Group 1(Control group) will be insufflated air during the colonoscopy; Group 2(Carbon dioxide group) will be insufflated carbon dioxide during the colonoscopy; Group 3(After appendectomy group) will be insufflated air during the colonoscopy. Since Group 1 is comparison group, the investigators will compare Group 2 to see if carbon dioxide gas insufflation can reduce the changes of intestinal microecology after colonoscopy. Meanwhile, compare Group 3 to see if the appendix can accelerate the recovery of intestinal microecology after colonoscopy.
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The intestinal microbiota composition
Timeframe: Before bowel cleansing, after colonoscopy, 7、14 and 28 days after the treatment