on duty

The man on duty rang an alarm.

值班警报。

The officers on duty were visibly overcome, many of them in tears.

那些值班官明显不能自持，许多人都流了眼泪。

Half the garrison are on duty.

有半数卫戍部队在执勤。

The patrol police on duty are on the alert against any possible disturbances.

"值班巡警处于戒备状态,随时准备付任何可能生骚乱。"

In addition to these arrangements, extra ambulances will be on duty until midnight.

除了这些安排以外，还增派救护车值班到午夜。

A policeman has to keep on his toes all the time he's on duty.

警察在执勤时必须时刻保持警覺。

The striped band round a policeman’s sleeve is to signify that he is on duty.

警察子上明他正在执勤。

Eight are on duty.

八个人在值班。

Six are on duty.

六个人在值班。