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

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.

Explanation:
Explanation/Reference:
Definition of OSPF areas: An OSPF network may be structured, or subdivided, into routing areas
to simplify administration and optimize traffic and resource utilization. Areas are identified by 32-bit
numbers, expressed either simply in decimal, or often in octet-based dot-decimal notation, familiar
from IPv4 address notation.
See discussion following Cisco Learning discussion.
https://learningnetwork.cisco.com/message/90832