有几种假说，包括地球变暖或变冷，季节波动或洋流的变化，以及大陆位置的变化。

There are several hypotheses, including warming or cooling of Earth, changes in seasonal fluctuations or ocean currents, and changing positions of the continents.

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因为移动和位置的变化太多。

Because they move and change place too much.

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第二个使用固定的地理方位，并不随我们本身位置的变化而变化。

The second system USES fixed geographic directions, which do not rotate with us wherever we turn.

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But luckily for us, there's a classical equation of motion that will, in fact, describe how the electron and nucleus change position or change their radius as a function of time.

但幸运的是，有一个,经典方程描述了电子和核子,位置或者它们直接的距离是,如何随时间变化的。

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That's what has changed between these two positions.

这就是在这两个位置间所发生的变化。

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Most frequently, chord changes come on the downbeat so composers signal to us in a fourth way the downbeat by means of chord change.

通常,和弦的变化都在重拍上,所以作曲家们用这第四种途径,通过和弦的变化告诉我们重拍的位置

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