Postpolypectomy bleeding is the most common major complication following a colonoscopic polypectomy procedure. The incidence rate ranging from 0.3 to 6.1%. Several preventive methods such as detachable snare and adrenaline injection have been proposed in the management of postpolypectomy bleeding in large colonic polyps. It has been demonstrated that administration of ascorbic acid (vitamin C) in abdominal surgeries could reduce the blood loss during the procedure, operation time and days of hospitalization. So the investigators designed a prospective, randomized study to compares the efficacy of vitamin C administration with application of prophylactic clip and detachable snare in the prevention of postpolypectomy bleeding in large polyps.