单项选择题
A.bdl/(bn+dm) B.bdl/(bm+dn) C.(bn+dm)/bdl D.(bm+dn)/bdl
A.宿主层 B.核心层 C.用户层 D.应用层
A.A,172.16.0.0 B.B,172.16.0.0 C.B,172.16.3.108 D.C,172.16.0.0