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A blackboard or a chalkboard is a reusable writing surface on which text or drawings are made with sticks of calcium sulphate or calcium carbonate, known...15 KB (1,627 words) - 20:21, 19 April 2024
 | A blackboard or a chalkboard is a reusable writing surface on which text or drawings are made with sticks of calcium sulphate or calcium carbonate, known... 15 KB (1,627 words) - 20:21, 19 April 2024 |