Cold polypectomy has the advantages of simple operation, less time-consuming and fewer complications. Guidelines have recommended cold snare polypectomy (CSP) to resect small polyps sized \<9 mm. CSP was designed to improve the complete resection rate and reduce adverse events. Investigators hypothesize that CSP is better than conventional hot snare endoscopic mucosal resection (HS-EMR) in the presence of injured submucosal arteries detected in the submucosal layer for 10-19 mm nonpedunculated colorectal polyps, resulting in lower delayed bleeding after CSP of 10-19 mm nonpedunculated colorectal polyps.