他始终保持着警惕。

He had remained alert the whole time.

各学校对此问题应该始终保持警惕。

Schools need to be constantly alert to this problem.

她用警惕的淡褐色眼睛快速扫视了一下房间。

Her alert hazel eyes flickered around the room.

一位警惕的警官发现了一辆满载炸药的卡车。

An alert police officer discovered a lorry full of explosive.

人们继续保持高度警惕。

The men proceed on high alert.