Source material: Primary source for all four librettos is Schott's 1899 vocal scores (republished in the United States by Schirmer in 1904).

资料来源：四个版本都来源于1899年schott出版的歌谱(该歌谱1904年在美国由Schirmer再版)。

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The wheel web, by virtue of its geometry and material characteristics, is a good emitter of high-frequency sound, and is believed to be the primary source of curve squeal noise.

尺寸和材料的特性导致了轮辋是一个良好的高频声源，轮辋也被认为是曲线尖啸噪声的主要来源。

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One material source of diamond is primary diamond mines and ancient placer in the ancient Yi River upstream in Shandong, the other is the primary diamond mine which may exist in this area.

金刚石的物质来源一是古沂河上游山东的金刚石原生矿和古砂矿，二是本区的可能存在的金刚石原生矿。

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"We've always had the philosophy that we're the primary source for this material, " he says.

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