在观察草履虫的应激性实验时：

（1）在载玻片的一端滴一滴清水，另一端滴一滴草履虫的培养液，并把这滴清水和这滴草履虫的培养液连通起来，用放大镜观察草履虫聚集在______．

（2）如果在草履虫的培养液的边缘放一粒食盐，用放大镜观察草履虫都聚集在______．

（3）上述实验说明了动物______，这个特性使它能趋向______刺激，逃避______刺激．

Border Gateway Protocol(BGP) is inter-autonomous system ______ protocol. BGP is based ona routing method called path vector routing. Distance vector routing is not a good candidate for inter-autonomoussystem routing because there are occasions on which the route with the smallest ______ count is not thepreferred route. For example, we may not want a packet through an autonomous system that is not secure eventhough it is shortest route. Also, distance vector routing is unstable due to the fact that the routers announce onlythe number of hop counts to the destination without defining the path that leads to that ______. A router thatreceives a distance vector advertisement packet may be fooled if the shortest path is actually calculated throughthe receiving router itself. Link ______ routing is also not a good candidate for inner-autonomous system routingbecause an internet is usually too big for this routing method. To use link state routing for the whole internetwould require each router to have a huge link state database. It would also take a long time for each router tocalculate its routing ______ using the Dijkstra algorism.

A．routing

B．switching

C．transmitting

D．receiving