因此，他们的第一个日历系统被自然地分为三个季节，每个季节都是根据河流的变化而划分：淹没期、下沉期和丰水期。

So, naturally, their first calendar was divided up into three seasons, each based on the river's changes: inundation, subsidence and harvest.

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CDC要求各公共健康实验室提供每个流感季节流行初期、高峰期和晚期的流感病毒标本，以及任何异常的标本。

CDC asks public health LABS to submit samples of flu viruses from the beginning, peak and end of each flu season, and any unusual samples.

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在北半球，我们现正进入季节性流感的高峰期。

In the northern hemisphere we are now entering the peak period for seasonal flu.

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