But he believes that theory, to be of use, must keep its feet on the ground.

但他相信，具有实用价值的理论必须要能与实际的生活情况相结合。

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Lombard next chose an unusually high and thick clump of brush, and cleared a small space three feet across in the centre of it, scattering twigs on the uncovered earth to keep off its chill.

伦巴第先生在一丛较厚的灌木中清出了一个三英尺见方的空地，让后将碎枝铺在地上隔绝寒冷的地气。

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On the eve of the debate the Greek Prime Minister George Papandreou said it was a "unique opportunity to keep the country on its feet".

BBC: Greece: The moment of truth

And Mr Shepherd said the company would keep its feet on the ground, despite its record performance.

BBC: Newcastle net record profit