Which of the following is the incorrect description of malignant ulcers? A: In posteroanterior view, the niche is round or unrepresentative round, surrounded by convex curves B: Relatively large cancerous ulcer with shallow depth C: In posteroanterior view, the contour of the niche is outwards, surrounded by concave curves D: Large areas of mucosal folds around the ulcer are destroyed and disappeared E: Mucosal folds are concentrated towards the niches, and they are interrupted halfway before they arrive