While troubleshooting some connectivity issues，you issue the “show ip ospf database”in order to ex amine the link state database. Which three of the statements below are true regarding the OSPF link state database（）

• A、Each router has an identical link state database.
• B、External routes are imported into a separate link state database.
• C、Syn chronization of link state databases is maintained via floodingo f LSAs.
• D、Information in the link state database is used to build a routing table by calculating a shortest-path tree.
• E、By default,link state databases are refreshede very 10 minutes in the absence of topology changes.