alert /əˈlə:t/ I. adj. 留神的，注意的：an alert mind 机警的头脑；be alert to danger 对危险保持警惕‖II. n.［u］&［c］警戒（状态），戒备（状态）；警报：a 24-hour alert 昼夜警戒 on (the) alert 处于警惕或警戒状态：be on full alert 处于全面戒备状态；go on (the) alert 进入戒备状态 Security forces were placed on alert.安全部队处于警戒状态。The government has put/placed the army on (the) alert.政府已命陆军进入战斗准备。‖III. vt. 向…报警，使警惕：An anonymous letter alerted police to the possibility of a terrorist attack at the airport.匿名信警告警方说恐怖分子有进攻飞机场的可能性。［考句］ The sign set up by the road alerts drivers to a sharp turn.路边的标志提醒司机留神急转弯。