短語詞組短語null modem line 空Modem線null modem cable line 一條串口通訊線geodesic null line [測]測地零線beam null line 射束零線null line suppression 空行抑制null -earth line 零線null line detection 零線檢查null line connection 接零null object reference at line 行空對象引用;在行空對象引用 返回 null line