A.1946 B.1957 C.1960 D.1964 E.1977
A.電報(bào)網(wǎng) B.電話網(wǎng) C.傳真網(wǎng) D.數(shù)據(jù)網(wǎng) E.模擬網(wǎng) F.數(shù)字網(wǎng)
A.用戶與電信網(wǎng)之間的接口設(shè)備 B.傳輸信號(hào)的信道