alert

一只小狗应该机警而活泼。

A young dog should be ___alert and playful.

当局对市中心发布了炸弹警告。

The authorities issued a bomb ___alert for the city centre.

已向沿海地区发布了恶劣天气警告。

A severe weather ___alert has been announced for the coastal regions.

教师需要对学生行为的突然变化保持警觉。

Teachers need to be ___alert to sudden changes in students' behavior.