Remember to be on the alert when walking at night.

夜晚走路时，记得提高警惕。

Everyone needs to be on the alert when camping in the wild.

在野外露营时，大家都需要提高警惕。

Our company has informed us that there have been many cases of piracy, and warned us to be on the alert.

公司已经通知我们，最近连续发生多起海盗袭击船舶事件，因此要求我港提高警惕。

Our company has informed us that there have been many cases of piracy, and warned us to be on the alert .

公司已经通知我们，最近连续发生多起海盗袭击船舶事件，因此要求我港提高警惕。

It is important to be on the alert for symptoms for H1N1, especially for seniors and those with a chronic health condition as they are more vulnerable to respiratory infection.

年长或患有长期疾病的人士较容易感染呼吸道疾病。因此他们需要特别留意有关甲型流感病症。