名词
中文翻译：封闭防御
同义词：
['closed fortification', 'closed siege', 'sealed defense']
例句：
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1. The city was closed down due to the outbreak of the epidemic.
由于疫情爆发，该城市被关闭。
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2. The soldiers were ordered to close their ranks and form a defensive line.
士兵们被命令排成一线，形成一道防线。
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3. The government has implemented a closed defence system to prevent any further attacks.
政府已实施封闭式防御系统以防止进一步的攻击。