We must build forces that are as impregnable as a rock.

我们必须建立坚如磐石的军事力量。

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The failure of the eradication programme created a belief, held by many, that malaria was impregnable to any kind of frontal attack.

消灭规划的失败令人产生一种信念，许多人均抱持这种信念，即任何正面攻击都无法击溃疟疾。

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Despite Microsoft's impregnable strength as a producer of software, its foray into hardware brings it up against two other considerable powers, both from Japan: Sony and Nintendo.

作为软件巨头，微软坚不可摧。但是，在硬件它上却碰到两位强大对手：日本的索尼和任天堂。

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India enjoyed a perfect start to the day, advancing a solid overnight position of 311-5 to a virtually impregnable one of 422-5 soon after lunch.

BBC: Krejza raises Australia's spirits

Certainly, given how poorly Mitt Romney has been doing at a time when the state of the economy should have handed him an impregnable lead, it is clear that the Republican party is going through a historic life crisis.

FORBES: Has David Brooks Defined a Turning Point for the Republican Party?

Its once impregnable popularity increasingly under pressure on other fronts, a long housing recession is the last thing it needs.

ECONOMIST: Housing