Don’t forget to turn on your radio at 7 p.m. this evening. We’ll be back then.
A. in the air
B. by air
C. on the air
D. off the air
网友回答
A. in the air
B. by air
(答案→)C. on the air
D. off the air
解析：这题考查介词短语，in the air在空中，by air乘飞机，on the air在播放 ，句意是：别忘了今晚7点打开收音机，那时我们将回来播放。选C。