提防；警戒著；随时准备著

警戒着， 随时准备着， 密切注意着

on the air───在广播，广播中

on the beat───合拍；在巡逻中

on the flat───没有让步条件的

on the slant───倾斜的

on the average───平均而言；一般说来

on the carpet───在考虑中；在审议中

on the market───上市；出售的

in the air───在空中；悬而未决；在流传中；不设防

on alert───警戒状态

She was always on the alert for some new calamities.───她总是保持警觉以防某种新的灾难.

They must be constantly on the alert for the enemy.───他们必须随时注意敌人.

Her fears had always been on the alert for an upheaval.───她日夜提心吊胆,严防突变.

These are the Chinese need to be on the alert.───这些都是需要中方警惕的.

They were constantly on the alert not to be taken by surprise.───他们一直处于常备不懈状态以防突然袭击.

Hearing this, I was instantly on the alert.───我一听这话, 当下就警惕起来.

The Armies were constantly on the alert not to be taken by surprise.───部队一直处于警戒状态以防突然袭击.

An early warning system puts everyone on the alert.───预警系统让每个成员进入警戒状态.

The policemen were on the alert for an excaped convict.───一名逃脱犯令警方全面警戒.

They want to be on the alert for similar buying opportunities.───他们要准备应对类似的购买机会。

The sentries were all on the alert.───哨兵们都警戒着.

Police are warning the public be on the alert for suspicious packages.───警方警告公众要警惕可疑包裹.

They did their best to keep on their guard [ on the alert ] .───他们尽量保持 警惕.

Police are warning the public to be on the alert for suspicious packages.───警方警告公众要警惕可疑包裹。

Drivers must be on the alert for traffic signals.───驾驶员必须密切注意交通信号.

Troops are on the alert against any possible aggression.───军队戒备着可能的来犯.

Knowing that danger threatened , the sentry was on the alert.───因为知道危险势将发生, 这哨兵加意戒备.

Drivers must be on the alert for traffic signals.