名词
中文翻译：Unknown
同义词：
['alert', 'warning', 'alarm']
例句：
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1. The air siren went off whenthe plane took off.
飞机起飞时，警报器响起了。
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2. The air siren wasa signal for everyone to get ready foran emergency.
警报器是紧急情况下的信号。
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3. Theair siren sounded as the plane landedsafely.
飞机安全着陆时，警报器响了。