protective gas保护气体protectiveadj.保护的；防卫的protective rejector circuit保护性抑制器电路Protective of radon in mine矿山防氡protective mask for workman工人保护面罩protective leather clothing防护皮衣Protective Security Service防毒安全勤务protective code of teletype电传保护码protective zero terminating保护接零protective devices to block防护挡车装置protective coal seam mining保护层开采protective farming technique保护性耕作