A.報(bào)文交換；虛電路；數(shù)據(jù)報(bào)
B.電路交換；報(bào)文交換；虛電路
C.電路交換；分組交換；數(shù)據(jù)報(bào)
D.電路交換；分組交換；報(bào)文交換

A.介質(zhì)可用帶寬與給定信號(hào)所需相匹配
B.介質(zhì)可用帶寬超過給定信號(hào)所需帶寬
C.介質(zhì)可用帶寬不是給定信號(hào)所需帶寬
D.介質(zhì)能達(dá)到的位傳輸速率超過傳輸數(shù)字?jǐn)?shù)據(jù)所需的數(shù)據(jù)傳輸率