Which of the following are true regarding OSPF areas?
1. You must have separate loopback interfaces configured in each area.
2. The numbers you can assign an area go up to 65,535.
3. The backbone area is also called area 0.
4. If your design is hierarchical, then you don't need multiple areas.
5. All areas must connect to area 0.

Loopback interfaces are created on a router, and the highest IP address on a loopback (logical) interface becomes the RID of the router but has nothing to do with areas and is optional, so (1) is wrong. The numbers you can create an area with are from 0 to 4,294,967,295 option (2) is wrong. The backbone area is called area 0, so option (3) is correct. All areas must connect to area 0, so option (5) is correct. If you have only one area, it must be called area 0. This leaves option (4), which must be correct; it doesn't make much sense, but it is the best answer.