北师大版高中英语模块7--Unit 20 New Frontiers 2
教程:北师大版高中英语模块7(选修)  浏览:585  
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    [00:01.56]Gunpowder

    [00:03.47]Gunpowder was invented by the Chinese

    [00:05.73]in the eighth century AD.

    [00:08.28]Early Chinese scientists discovered

    [00:10.64]that they could make an explosive substance

    [00:12.76]by mixing sulphur,charcoal and saltpeter.

    [00:16.76]Gunpowder was used in warfare

    [00:18.93]and led to the development of many different

    [00:21.00]kinds of weapons.

    [00:22.77]For example, rockets carrying an explosive

    [00:25.28]shell of gunpowder could be launched

    [00:27.98]at enemy soldiers from a bamboo tube.

    [00:32.08]The Compass

    [00:33.66]The ancient Chinese noticed

    [00:34.96]that certain kinds of metals,

    [00:36.95]like iron ore, usually aligned themselves

    [00:39.39]in a north to south position.

    [00:41.84]By the third century,

    [00:43.17]they had started making the first,

    [00:44.84]simple compassesby floating small pins

    [00:47.92]of magnetic metal in bowls of water.

    [00:50.74]By the eleventh century,

    [00:52.11]the Chinese were using sophisticated

    [00:54.05]compasses to navigate their ships at sea.

    [00:57.90]In the West magnetism was not discovered

    [01:00.42]until the fifteenth century.

    [01:02.65]Until this time, European sailors

    [01:04.83]were still navigating by the stars.

    [01:06.56]

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