在这里必须有一种方式去向对象发出一个请求，在对象收到请求后才能照指令去完成一个事务，在屏幕上打印一些东西，或是打开一个开关。
There must be a way to make a request of that object so it will do something, such as complete a transaction, draw something on screen or turn on a switch.
万一发生识别错误，只要踩下脚踏开关，就可以使指令消除。
In case a wrong recognition is made, the command can be cancelled by simply pressing the foot switch.
调制解调器没有接受发送给它的指令。验证该调制解调器是否接线正确并且打开了电源开关。
The modem did not respond to the command sent to it. Verify that the modem is properly cabled and powered on.
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