如果有自动应答器，可以建立确认列表，最好是双向确认列表。
If you have an Autoresponder to build an Opt-In list, use a double Opt-In.
车-地之间双向传输，信息闭环确认；
Two way transmission between the train and ground facilitates closed-loop acknowledgement.
车-地之间双向传输，信息闭环确认；
Two way transmission between the train and ground facilitates closed-loop acknowledgement.
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