根据下面的文字资料回答 71～75 题 n the following essay，each blank has four choices．Choose the most suitable one from the four choices and write down in the answer sheet．
Open Shortest Path First(OSPF)is a（ 1 ）routing algorithm that（ 2 ）work done on the OSI IS-IS intradomain routing protocol．This routing，as compared to distance-vector routing，requires（ 3 ）processing power．The Dijkstra algorithm is used to calculate（ 4 ）OSPF routing table updates only take place when necessary，（ 5 ）at regular intervals．
第6题：文中（ 1 ）处正确的答案是（ ）。
A．distance-vector
B．link-state
C．flow-based
D．selective flooding
