•I'm not feeling very alert today - not enough sleep last night!今天我感觉特别迟钝——昨晚没睡好！

•A couple of alert readers wrote in to the paper pointing out the mistake.有几个眼尖的读者给报社写信，指出了这个错误。

•Parents should be alert to sudden changes in children's behaviour.父母应该对孩子行为的突然变化有所警觉。

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•a bomb alert炸弹警报

•The army was put on (full) alert as the peace talks began to fail.当和谈快要破裂的时候，军队进入（全面）戒备状态。

•The public were warned to be on the alert for (= watching carefully for) suspicious packages.有关部门提醒公众，要对可疑包裹加以警惕。

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•An anonymous letter alerted police to the possibility of a terrorist attack at the airport.有人给警方写了一封匿名信，警告机场可能会受到恐怖袭击。