Which of the following describes the roles of devices in a WAN?（）

• A、A CSU/DSU terminates a digital local loop.
• B、A modem terminates a digital local loop.
• C、A CSU/DSU terminates an analog local loop.
• D、A modem terminates an analog local loop.
• E、A router is commonly considered a DTE device.
• F、A router is commonly considered a DCE device.