From the style we use the quotations, they are overtly use and covertly use ;

从用典的方式上看，引用典故有明引和暗引；

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In theory, the Army could use such a system to approach targets covertly and drill through concrete, steel, wood, or other materials from a stand-off distance equal to the length of a football field.

理论上，美国陆军将利用该系统实现某些目标，既通过远距离(超过一个足球场的距离)的设备对混凝土、钢铁、木头以及其他材料进行隐蔽的击穿作业。

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