I feel sorry for the beggars, but I can't stand it when they teach their children how to beg.
我很同情乞丐,但我真的看不惯他们教孩子怎么样行乞。
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。