The nominal head was presented for preliminary selection of hydraulic models, with consideration of the efficiency and reliability at all operation conditions.

为了兼顾各种特征扬程工况下的运行效率和可靠性，在水力模型初选阶段提出了选型名义扬程的概念。

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Jeff: I was told that with the increasing Numbers of the participants, they started to undertake preliminary selection contest in each continent, the winners could take part in the final.

杰夫：我听说过，此后随着参赛国家数量的不断增多，便开始在各大洲进行分区预选赛，优胜者参加最后的决赛。

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Usually some hypothesis is a necessary preliminary to the collection of facts, since the selection of facts demands some way of determining relevance.

通常，有某种的假说是收集事实的必要先决条件，因为在对事实的选择上，要求有某种方法确定事实是否与题有关。

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