be on the alert的用法和樣例：
例句
- Fasten on what the teacher is saying.
注意聽老師說。 - She always wants to be the focus of attention.
她老想成為人們注意的中心。 - Be on the watch for thieves in this crowd.
提防人群中有小偷。 - Be sure to be watchful or alert.
必須留神，千萬要提防。 - Keep a vigilant eye on the imperialist jackals.
對帝國主義的走狗要保持警戒。 - My reins also instruct me in the night seasons.
我的心腸在夜間也警戒著我。
