在广播或者NBMA网络中，DR和DROther建立邻接关系，BDR也和DROther建立邻接关系，DR和BDR之间不需要建立邻接关系。（）

A.所有DRother只与DR和BDR建立邻居关系

B.在广播网络中，必须选举DR和BDR，没有DR和BDR中的任何一个，广播网络都不能正常工作

C.DRother监听的组播地址为224.0.0.5

D.DRother监听的网络地址为224.0.0.6

B.在广播和NBMA以及point-to-muiltipoint类型的接口上才会选举DR

C.DR是指某个网段中概念，是针对路由器的接口而言的。某台路由器在一个接口上可能是DR，在另一个接口上可能是BDR，或者是DROther。

D.两台DROther路由器之间不进行路由信息的交换，也不会互相发送HELLO报文。

B.Backup

C.DR

D.DROther

B、双向

C、loading

D、established

A．Ask Dr. Smith to call the library.

B．Ask Dr. Smith to alter his decision.

C．Get Dr. Smith's written permission.

D．Get the book directly from Dr. Smith.

A．错误

B．正确

A．The student cannot choose the time.

B．Dr. Roberts may tell the student the answer.

C．Dr. Roberts is the dean of the School of Economics.

D．She does not want to answer the student's question.

A．The boy became better.

B．The boy died.

C．The boy disappeared.

A．The visiting economist has given several lectures.

B．Dr. Johnson and the guest speaker were schoolmates.

C．Dr. Johnson invited the economist to visit their college.

D．The guest lecturer's opinion is different from Dr. Johnson's.

A．The visiting economist has given several lectures.

B．Dr. Johnson and the guest speaker were schoolmates.

C．Dr. Johnson invited the economist to visit their college.

D．The guest lecturer's opinion is different from Dr. Johnson's.