Rosa knows she is the eldest of the three children in the family, and she must work hard to _______ the other two. So she does.

A．set an example to

B．make the most of

C．take a look at

D．play a trick on

电视频道的中频转换方式是将某频道的射频信号（）为中频信号，中频频率为（）MHz，然后再将它变换为待转频道的射频信号。