on duty

值班，上班

on (the/an) average, on a large scale, on a level with, on a river, on a small scale, on a weekly (daily basis), on account of, on an average, on an even keel, on and off, on average, on balance, on behalf of, on board, on business, on condition that, on credit, on cue, on diet, on display, on earth, on end, on file, on fire, on foot, on guard, on hand, on instalments, on instinct, on no account, on occasion, on one's guard, on one's head, on one's honor, on one's honour, on one's own, on one's way to..., on order that, on principle, on purpose,