【单选题】Your f ir m has been referred to us by the ABC Co. of Pakistan, __ we have done business for many years. A. which B. with that C. whom D. with whom
【简答题】变频器的干扰主要有哪些?在超外差接收机中,中频f I =f L -f s =465kHz,试分析下列现象: (1)在某地,当收音机收听1090kHz的信号时,还能听到1323kHz的电台播音; (2)当收音机接收1080kHz的信号时,还能听到540kHz台的播音; (3)当收音机接收580kHz的信号时,还能听到1510kHz台的播音; (4)当收音机接收931kHz的信号时,伴有音...