海洋表面的水位，尤其是在平均高水位和低水位之间的平均位置的水位，用作计算陆地海拔和海水深度的标准。

The level of the ocean's surface, especially the level halfway between mean high and low tide, used as a standard in reckoning land elevation or sea depths.

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近几年，威尼斯的高水位平均每年导致100场洪水。

In recent years, Venice's acqua alta, or high water, has resulted in an average of 100 floods a year.

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So, for example, we have this average level, and then it can go high where we have the peak, or it can go very low. We can also discuss sound waves, so again it's just the periodic variation of some property -- in this case we're talking about density, so we have high density areas and low density areas.

例如这是平均位置，在峰的位置水位高，在谷水位低，我们也可以,讨论声波它也是某种,量的周期变化，在这里我们,讨论的是密度,我们有高密度区和低密度区。

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