on duty

The man on duty rang an alarm.

班员发警报。

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

那些班官员明显不能自持，许多人都流泪。

Half the garrison are on duty.

有半数卫戍部队在执勤。

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

除这些安排以外，还增派救护车班到午夜。

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

"班巡警处于戒备状态,随时准备应付任何可能发乱。"

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.

警察袖子上袖标标明他正在执勤。

Eight are on duty.

八个人在班。

Six are on duty.

六个人在班。