—Shall we go out for dinner tonight? —__

小明要在地图上查找联合国总部所在地，应选择下列哪个国家的地图

A．美国

B．比利时

C．瑞士　

D．英国

17，8，15，6，13，4，12，( )

A．13

B．1

C．15

D．2

Open Shortest Path First (OSPF) is a (66) routing algorithm that (67) work done on the OSI IS-IS intradomain routing protocol. This routing, as compared to distance-vector routing, requires (68) processing power. The (69) algorithm is used to calculate routes. OSPF routing table updates only take place when necessary, (70) at regular intervals.

A．distance-vector

B．link-state

C．flow-based

D．selective flooding

选择阀件的依据是什么？

远缘杂种不育的原因及其克服方法？