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