Bristles with a variety of heights are used to give an overall "medium" rating. 混合不同高度的刷毛，調制出軟硬度適中的刷頭。
By sending satellites round the earth at different heights,we can find out how much air there is at each height. 我們把衛星送入不同高度的軌道饒地球運行，就能測出地球上空不同高度處空氣的含量。
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