er, breakdole, II. Read and understand each question below.Encircle the letter of the correct answer. 21. When is a material useful? A. When the material serves a purpose C. When the material hazards B. When the material brings harm D. When the material is toxic 22. When is a material harmful? A. When the material can be used many times. B. When the material can be used in cooking. C. When the material gives other uses aside from its purpose. D. When the material brings danger to people and environment​