O字母开头的单词或词组(第7页)：
- operational
- optimize
- offense
- off and on
- on a large scale
- on average
- on a small scale
- on account of
- on one hand
- on condition that
- on guard
- on fire
- on hand
- on occasion
- on schedule
- on second thoughts
- on the contrary
- on the ground of
- on the point of
- on the road
- on the spot
- once for all
- out of control
- out of date
- out of doors
- out of place
- out of the question
- out of touch
- out of practice
- one day
- on holiday
- over here
- one by one
- Onions
- Ouch!
- on Sunday afternoon
- on duty
- overjoyed
- over and over
- only a little
- once a week
- out of sight
- once again
- Olympic