名词
中文翻译：在服役中
同义词：
['on duty', 'on standby']
例句：
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1. The soldier was on service when the enemy attacked.
当敌人攻击时，士兵正在待命。
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2. She's on service at the moment, so she can't be reached.
她现在在待命状态，所以联系不上。
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3. The police were on service to help the injured.
警察在待命状态，以帮助受伤的人。