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