多项选择题 When designing OSPF networks，it is not recommended to have an excessive number of routers in any single area.Which two of the following statements describe the consequences of having too many routers in an area（）。

多项选择题 OSPF协议定义了5种网络类型，哪些类型的网络需要选举网络Designated Router（DR）、BackupDesignated Router（BDR）（）？

多项选择题 You are the administrator of the large OSPF network and are considering dividing it to multiple areas.What are two advantages of configuring multiple OSPF areas（）？