单项选择题
A.20 B.21 C.22 D.23
A.77.0.5.5 B.40.40.0.254 C.66.40.90.121 D.72.40.91.1
A.1000Base-CX B.1000Base-TX C.1000Base-SX D.10Base-T E.1000Base-T F.1000Base-LX