Respuestas

2012-11-26T22:22:42+01:00

the blackboard is white

 

the lenses is of diferent colours example red

¡La mejor respuesta!
2012-11-26T22:24:48+01:00

Is made of sticks of calcium sulfate or calcium carbonate

A blackboard can simply be a piece of board painted with matte dark paint (usually black or dark green).

A more modern variation consists of a coiled sheet of plastic drawn across two parallel rollers, which can be scrolled to create additional writing space while saving what has been written.