Which of the following describes the roles of devices in a WAN?()
A、A.A CSU/DSU terminates a digital local loop.
B、B.A modem terminates a digital local loop.
C、C.A CSU/DSU terminates an analog local loop.
D、D.A modem terminates an analog local loop.
E、E.A router is commonly considered a DTE device.
F、F.A router is commonly considered a DCE device.