/əˈlɜ:t ||; əˈlɝt/adjalert (to sth) watching, listening, etc for sth with all your attention 留心的；留神的；警觉的: Security guards must be alert at all times.保安人员必须时刻保持警惕。to be alert to possible changes留意可能出现的变化
alert²
/əˈlɜ:t ||; əˈlɝt/noun [C] a warning of possible danger 警报: a bomb alert炸弹警报on the alert (for sth) ready or prepared for danger or an attack 警惕；戒备
alert³
/əˈlɜ:t ||; əˈlɝt/verb [T] alert sb (to sth) to warn sb of danger or a problem 警告；提醒