be on guard against;watch out for;be vigilant;be on the alert;guard ;

The blackbird had a quick, wary look in case the cat was anywhere around.
这只乌鸫迅速警惕地张望了一眼,以防那只猫就在附近。
来源:《柯林斯高阶英汉双解学习词典》He warned the public to be vigilant and report anything suspicious.
他警告公众要提高警惕,遇到任何可疑情况都要报告。
来源:《柯林斯高阶英汉双解学习词典》
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