OSPF routing uses the concept of areas. What are the characteristics of OSPF areas?（）

• A、Each OSPF area requires a loopback interface to be configured. 
• B、Areas may be assigned any number from 0 to 65535.
• C、Area 0 is called the backbone area.
• D、Hierarchical OSPF networks do not require multiple areas.
• E、Multiple OSPF areas must connect to area 0.
• F、Single area OSPF networks must be configured in area 1.