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 cutural tool. It is usually made of wooden boards four to five eenlimeters thick in the shape of a rectangle. It is painted black on the surface with black pednt. 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 varicty of blaekboards 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.

The blaekboard is so common and unattractive in our life, yet it has played an important role in our study, Our teachers have written equation after equation and solved countless problems on it. It is such a common rectangular blackboard, but it is the golden key to the door of the treasure house of knowledge.