练习系统功能调用（屏幕清屏、光标坐标、字符字串显示、键盘读取）和过程调用与宏指令。显示年月日，时分秒，并按某键开始计时。-Practice system function call (screen screen clearing, the cursor coordinates, and character string display, keyboard read) and procedure calls and macro instruction. Display date, determin