free frequency

例句：

1. 1.The free frequency of the radio waves is measured in hertz.
   无线电波的自由频率是以赫兹为单位测量的。
2. 2.The free frequency of the radio waves is measured in hertz.
   无线电波的自由频率是以赫兹为单位测量的。
3. 3. The free frequency of the radio waves is measured in hertz.
   无线电波的自由频率是以赫兹为单位测量的。