目前关于PCD的发病率不同文献的结果不同，也未见PCD危险因素的研究报道。

But there were respective results of PCD incidence in different literatures, meanwhile, there was no study to analyze risk factors of PCD.

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不同文献资料对空气过剩系数计算方法的不同，在不少场合下造成了一些概念和数值上的混乱。

Different methods for excess air coefficient given in different literatures have made confusions in the concept and values of excess air.

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So what people have written in different languages about the things that we read.

也就是人们用不同语言编写的有关我们所阅读的著作(的文献)。

主修古典文学 - SpeakingMax英语口语达人