Anyone who has ever been to school would have seen many blackboards big and small on which characters in different colors of chalk are written.The blackboard is a kind of cultural tool. It is usually made of wooden boards four to five centimetres thick in the shape of a rectangle.It is painted black on the surface with black paint. Underneath there is a groove for dust.With the development of the educationaI cause, there has been an increasing development in cultural facilities and equipment.The variety of blackboards is on the rise. There are glass-made blackboards, velvet blackboards made on the basis of the function of statics, magnetic black-boards made according to the function of magnetics, etc.

　　任何到过学校的人，总见过许多大大小小的，上面写着各种颜色粉笔字的黑板。黑板是一种常见的文化工具，它一般呈矩形，用本质夹板做成，厚四五厘米。它的正面涂上黑漆，下面还有一条积灰槽。教育事业的发展，促进了文化用品的发展。黑板的品种不断增多，有玻璃黑板，有根据静电作用造出的绒布黑板，有根据磁性作用造成的磁性黑板……