Signals are different in that they cannot return anything: there is neither a "signal return" message, nor any other type of error message.

信号的不同之处在于它们不返回任何内容：既没有“信号返回”消息，也没有任何类型的错误消息。

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The strongest return signal came from clouds.

最强的返回信号来自云层。

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That could signal a return to the era of monopolies in some markets, with the risk that entire countries could be held ransom by their service providers, the authors warned.

作者警告，那可能预示着部分市场返回到垄断时代，整个国家可能有被其服务提供商劫持而勒取赎金的风险。

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The worry for the British is that this incident may signal the return of a tactic used years ago by Irish Republican militants: pre-meditated attacks on British soldiers inside England.

NPR: Murder In South London Treated As Terrorist Attack

Adjusted targets signal a return to the past.

FORBES: Incentivizing Michael Eisner

By picking up this return signal, the radar probe's own antenna collects information about the crystal and, thus, the physical state of the tyre.

ECONOMIST: MONITOR