The annual rings of a tree are visible circles one after another, and those of a man are invisible circles of worries.

树的年轮是一个个有形的圈圈；人的年轮是一圈圈无形的心事。

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The agent distributes the server objects (which appear as circles filled with color) around an invisible circle of set radius.

代理程序把服务器对象(用着色的原型表示)分散在不可见的设定半径的圆上。

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Circles of people would fall back at the waist while a man in the centre shot an invisible machine gun.

BBC: A little liquid courage in Cali, Colombia