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Well, one way to think about it is imagine that you are walking on c, on the rim of this cone. You have two options.

一种办法就是想象你沿着C走，沿着圆锥的边走，你有两种走法。

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Retinas use two main types of light-sensitive cells to allow animals to see: Rod cells help measure brightness, while various types of cone cells help distinguish colors.

动物主要借助网膜中的两类光感细胞获得视觉：视杆细胞帮助感知亮度，而种类众多的视锥细胞则帮助辨别颜色。

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The five two-way speakers each hold two three-inch drivers and a one-inch tweeter, while each of the two 70 watts-per-channel active subwoofers has a roughly eight-inch cone.

FORBES: Sounding Out Home Theater

Yet noble intentions do not, of themselves, move concrete, even rotting concrete like the cement-and-pine-cone slurry used to make the Elwha Dam, the first of the two structures to be built.

ECONOMIST: Water in the West (2)