Which statement is correct about logical units on Juniper Router interfaces?()
A、A.Logical units are used only when a Layer 2 identifier is present such as a VLAN
B、B.A logical unit of 0 is required when using a frame-relay DLCI
C、C.A logical unit is always required
D、D.Logical units are not required unless ATM or 802.1Q VLAN tagging is configured.