Sometimes, by buying something cheap now, you will be costing yourself more in the long run.
有时候你花了很少钱买了便宜货,但它日后可能要花掉更多的钱。
This depends on the precise radio frequency of the 21-cm wavelength, or 1420 megacycles per second.
这种通讯联系要靠21厘米波段,即每秒1420兆周的精确无线电频率。