根据材料回答下面的题目：{Page}Border Gateway Protocol (BGP)is inter-autonomous system ___(71 )__protocol. BGP is based on a routing method called path vector routing. Distance vector routing is not a good candidate for inter-autonomous system routing because there are occasions on which the route .with the smallest__(72)__count is not the preferred route. For example, we may not want a packet through an autonomous system that is not secure even though it is shortest route. Also, distance vector routing is unstable due to the fact that the routers announce only the number of hop counts to the destination without defining the path that leads to that____(73)___. A router that receives a distance vector advertisement packet may be fooled if the shortest path is actually calculated through the receiving router itself. Link____(74)__routing is also not a good candidate for inner-autonomous system routing because an internet is usually too big for this routing method. To use link state routing for the whole internet would require each router to have a huge link state database. It would also take a long time for each router to calculate its routing____(75)____using the Dijkstra algorithm.{Page}A．routingB．switchingC．transmittingD．receiving

A. status
B. search
C. state
D. research