onprep.在 ... 之上；由 ... 支撑着；在（某一天）；关于；基于adv.穿着；向前（移动)；表示持续性adj.表示已连接、处于工作状态或使用中；发生；值班ONRON欧姆龙可编程控制器

1. Fasten on what the teacher is saying.
   注意听老师说。
2. I noticed scores of sorrow on her face.
   我注意到她脸上悲痛的痕迹。
3. Be on the watch for thieves in this crowd.
   提防人群中有小偷。
4. Be sure to be watchful or alert.
   必须留神，千万要提防。
5. Keep a vigilant eye on the imperialist jackals.
   对帝国主义的走狗要保持警戒。
6. My reins also instruct me in the night seasons.
   我的心肠在夜间也警戒着我。
7. Wherever they went she was evidently always on the watch.
   很明显，无论他们到什么地方，她时时刻刻都在警惕着。
8. Knowing that danger threatened, they were on the alert.
   因为知道可能会发生危险，他们处于戒备状态。
9. These networks are on the alert for warning signs that show the weakening of rock layers that can precede an earthquake.
   这些网络始终处于戒备状态，搜索地震前岩石可能松动的警告迹象。