Drivers must be on the alert for traffic signals.

驾驶员必须密切注意交通信号.

《简明英汉词典》

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.

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These are the Chinese need to be on the alert.

这些都是需要中方警惕的.

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The city must be on the alert for being polluted.

城市要防止污染.

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They should also be on the alert for the attack of typhoon.

此时,沿海居民应著手努力农耕和渔业,也应开始警觉台风来袭.

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Passengers on buses should be on the alert against pick - pockets.

公共汽车上的乘客应提防扒手.

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Drivers be on the alert for traffic signals.

司机必须注意交通信号.

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You should be on the alert to any sudden change in the situation.

你们要对形势的突变有足够的准备.

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I believe that days of the turnover dropped investors should be on the alert.

笔者认为,近两日成交金额的骤减应该引起投资者的高度警惕.

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Twice a week or two more than this feeling be on the alert.

每周两次或两次以上出现这种感觉,就应引起警惕.

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