Close a instead, and a similar pattern will form behind slit b.

关闭A，粒子就会通过裂缝B并且形成类似的形状。

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So now if I take, see, I can form a single closed curve that will enclose all of this region with kind of an infinitely thin slit here counterclockwise.

如果这么做的话，就能得到区域上的一条闭合曲线,它包围了这个区域。

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The lower and upper walls match mutually to form a horizontal slit, which preven the light from being reflected by the tape and prevent the misreading of optical detector outside the cassette.

该上、下壁互相配合而形成一水平准直狭缝，以确保光源发出的光不在磁带上方或下方反射而引起位于磁带盒外的光检测器的误读。

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