Hold the floss tightly against the tooth, and move it away from the gum. Slide it firmly down the tooth surface, combining this with a back-and-forth motion.

牙线紧紧地贴着牙齿，往上向远离牙龈的方向移动，再沿着牙齿邻面向下移动，把这个动作跟牙线的前后移动组合在一块。

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The long serrated knife is often called a bread knife because it is particularly good for slicing breads that require a back and forth sawing motion.

长齿刀经常被称为面包刀，因为人们在切面包时需要前后锯着切面包，长齿刀很适合这个工作。

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The spins are then repeatedly flipped, causing the cantilever to gently sway back and forth in a synchronous motion.

这些磁旋反复的翻转，从而导致硅悬臂出现轻微的同步摆动。

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For the moment, the back-and-forth motion is occurring as the market continually tries to gauge how the European debt saga will play out.

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