It is an anonymous letter.

这是一封匿名信.

《简明英汉词典》

The president is said to receive an anonymous letter yesterday.

听说总裁昨天收到一封匿名信.

辞典例句

We received an anonymous letter.

我们收到一封匿名信.

辞典例句

Who wrote the letter? I don't know. It was an anonymous letter.

这封信是谁写的? 我不知道. 这是一封匿名信.

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There days after Rastus'disappearance, Mrs. Ramsay received an anonymous letter.

在拉斯图失踪的三天后, 拉姆齐女士收到了一封匿名信.

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The president was shocked because he received an anonymous letter which contained some pungent problems.

总统收到了一封匿名信,里面有一些很尖锐的问题,这让他感到很震惊.

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