Chalk produce, and thus widely used in the developing world, calcium-based chalk can be made where the crumbling particles are larger and thus produce less dust, and is marketed as "dustless chalk". Colored chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often colored), used to draw on sidewalks, streets, and driveways, are primarily made of gypsum. Chalk is a source of quicklime by thermal decomposition, or slaked lime following quenching of quicklime with water. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines,
Blackboard Inc. the deployment options of Blackboard Learn to include public cloud, and improvements to Blackboard's mobile app. , Blackboard serves approximately 17,000 schools and organizations. It holds the highest share of the education market with 75 percent of colleges and universities and more than half of K-12 districts in the US using its products and services. , Blackboard had acquired MyEdu, Perceptis, and CardSmith, and Requestec under Bhatt's leadership. The acquisitions reflected Bhatt's new acquisition strategy of making investments that serve students and will lead to innovations in Blackboard's core teaching and learning products. Blackboard has used the acquisition of other