A.移動(dòng)電話網(wǎng) B.公用電話網(wǎng) C.公眾網(wǎng)路 D.國內(nèi)電報(bào)網(wǎng)絡(luò)
A.3 B.4 C.5 D.6
A.數(shù)字?jǐn)?shù)據(jù)網(wǎng) B.綜合數(shù)字網(wǎng) C.數(shù)據(jù)通信分組網(wǎng) D.公用數(shù)據(jù)網(wǎng)