Open Shortest Path First(OSPF)is a (71) routing algorithm that (72) workdone on the OSI IS-IS intradomain routing protocol．This routing，as compared todistance—vector routing，requires (73) processing power．The Dijkstra algorithm is usedto calculate (74) OSPF routing table updates only take place when necessary， (75) atregular intervals．

A:derivedfrom B:deviatedfrom C:was derived from D:was deviated from