Which of the following are characteristics of OSPF areas?（）

• A、Hierarchical OSPF networks need to be in one area
• B、Multiple OSPF areas must connect to area 0
• C、Single area OSPF networks must be configured in area 1
• D、Areas can be assigned any number from 0 to 63535
• E、Area 0 is called the backbone area
• F、Each OSPF area need to be configured with a loopback interface