这是一种机械式的传播，包含信号旗、21响礼炮、号角、汽笛。

This is the mechanical type of communication, which includes the use of signal flags, the 21-gun salute, horns, and sirens.

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信号可以用旗帜、灯光、汽笛和枪声来表示。

A signal may be given by means of flags, lights, sirens and guns.

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信号可以用旗帜、灯光、汽笛和枪声来表示。

A signal may be given by means of flags, lights, sirens and guns.

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