We must be alert to the possibility of danger.

我们必须认识到危险的可能性。

《牛津词典》

We must be alert to these signals and respond with the compassion and care that are hallmark traits of what it means to be a woman, anywhere, everywhere.

我们必须警惕这些信号，以同情和关爱来回应，这些信号是标志性特征，说明在任何地方、在所有地方做女人意味着什么。

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Be alert to this.

对此要保持高度的警觉。

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The U.S.State Department has issued a fresh travel alert for India, saying the U.S.government continues to receive information that terrorist groups may be planning attacks here.

VOA: standard.2009.10.30

Because it's a very intense job they have to be alert every moment.

因为是高度集中的工作,他们需要时刻保持警惕。

普林斯顿公开课 - 国际座谈会课程节选

"With that,I expect the security agencies to be 24-hours alert.

VOA: standard.2009.07.30

Policy makers must also be alert to several other necessary components of health-care sustainability.

WSJ: How Asia Can Get Health Care Right

That's why parents need to be alert to symptoms in themselves as well as their children, says Patti.

CNN: 10 infants dead in California whooping cough outbreak

Obviously, we are concerned enough to alert those that are in Europe to be alert to their surroundings.

WHITEHOUSE: Press Briefing