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單項選擇題

You have just obtained a modular Cisco router with 2 serial connections and a BRI/U interface. What other physical piece of hardware is required in order to establish an ISDN connection?（）

A. Nothing. The router is already suitable.
B. A BRI WAN interface in the router.
C. An external NT1 to terminate the local loop.
D. A TA/NT1 device on the router.

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