1. [单选题]当配置一个CISCO的路由器时，缺省的DR和BDR优先级是（）。
B. 1
C. 16
D. 255
2. [多选题]With regard to Ethernet media access methods, which of the following are true?(Choose all that apply.)
A. A device waits for an electronic signal before transmitting.
B. A device listens and waits until the media is not busy before transmitting.
C. All devices on an Ethernet segment see data that passes on the network medium.
D. Only the sender and the receiver devices see data that passes on the network medium.
E. Ethernet networks allow you to configured devises with higher transmission priority.
3. [单选题]以下特殊区域中哪一个没有自动下发缺省路由（）
A. 末梢区域
B. 完全末梢区域
C. NSSA区域
D. 完全NSSA区域
