索款信的一种形式是拖欠债务催告信。

One form of collection letter is a letter of delinquency.

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一种电路状态信令形式。其中，电路状态由一个或多个信令状态比特显示，这些比特不断重复发送并与特殊电路相关联。

A form of circuit state signaling in which the circuit state is indicated by one or more bits of signaling status sent repetitively and associated with that specific circuit.

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书写有力度的感谢信并不仅仅是一种形式。

Writing powerful thank-you letters is not just a formality.

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