请注意，本文编写于 850 天前，最后修改于 752 天前，其中某些信息可能已经过时。
On the air: broadcast, transmitted, or shown on TV or radio.
our favorite singer is __ right now. Switch on the TV!
on the fence: undecided, unsure, uncertain
Jack: Have you decided which university you're joining?
Chloe: No, I'm still __________.
on the warpath: very angry, ready to fight, ready to go to battle
The parents are __ since they heard about the big increase in school fees.
on the level: honest, truthful, straightforward
The interviewer was __ about why they could not hire me. It seems you must have a PhD to get that position.
on the ball: very good, competent, alert, knowledgeable
Wow, you're really __ today! That was the best speech I've ever heard you deliver.
on the sly: secretly, deceptively, without anyone knowing
Mary and Bill were seeing each other __________. Their spouses didn't know anything about it.
on the mend: recovering, healing, getting better
Jim: Hey, how's your grandfather now? Is he out of the hospital?
Bob: Yes, he's back home and __________. Thanks for asking.
on the fritz: not working, broken
I was really annoyed because my laptop was __ this morning. I couldn't finish my report.