一个“黑板”的程序，界面上有粉笔和板擦，用户可以使用粉笔来划线，或者使用板擦来擦除黑板上书写的内容。同时黑板还支持文字输入。-A " blackboard"　process, interface with chalk and eraser, the user can use chalk to dash, or use eraser to erase the contents of the writing on the blackboard. At the same time Blackboard also supports text input.