抢答器的实现，当按下任一个按键后，其他的按键都没有效果，系统自动只识别接收到的第一个信号，并在数码管上显示出来，重新启动后开始下一轮抢答-Responder realization, when you press any button, the other buttons have no effect, the system automatically recognizes only the first received signal and the digital tube display,