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阅读理解
How could we tell time if there were no watches or clocks anywhere in the world?
The sun was probably the world’s first“clock”, except in the far north, where the Eskimos(爱斯基摩人)live．There, it’s dark most of the winter, and light most of the summer．But in most of the world, people have used the sun fooday, if you don’t have a clock that shows time, you still know that when the sun shines, it’s day, and when it’s dark, it’s night．The sun can not only tell you whether it’s day or night but also it’s morning, noon, or afternoon．When the sun is almost directly overhead, it’s noon．
People who live near the sea from the tides．In the daytime, for about six hours, the water rises higher and higher on the beach．And then it about six hours．The same thing happens again at night．There are two high tides and two low tides every 24 hours．
Seamen on a ship leall time by looking at the moon and the stars．The whole sky is their clock．In some places in the world the wind comes up at about the same time every day or changes direction or stops blowing．In these places the wind can be the clock．
A sand clock is an even better clock．If you had fine dry sand in a glass shaped like the one in the the sand will take another hour to go back again．
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