How can a network administrator secure rest APIs?

Refer to the exhibit. A network engineer notices PE-21 convergence degradation due to the growing LSDB size of Level 2 areas in the network. The engineer decides to migrate router PE-21 from an inter-area design to an intra-area implementation. Inter-area routing must be accomplished via an ATT-bit set by the Level 1/Level 2 router. Which configuration must the engineer implement on PE-21 to complete the migration?

Drag and drop the OSPF area types from the left onto the correct statements on the right

Refer to the exhibit. While troubleshooting the OSPF adjacency between routers R1 and R2, an engineer noticed that both routers are stuck in the EXCHANGE/EXSTART state. What should the engineer fix to solve the ongoing issue?

Refer to the exhibit:

Which configuration prevents the OSPF neighbor from establishing?