Which of the following is true about an OSPF area border router (ABR)?（）

• A、The ABR must have multiple interfaces connected to the backbone areA
• B、An ABR is a router with two interfaces, each connected to a different nonbackbone areA
• C、The only requirement to be considered an  ABR is at least one interface connected to the backbone areA
• D、An ABR must have at least one interface in the backbone area plus at least one other interface in a nonbackbone areA