【单选题】

Open Shortest Path First(OSPF)is a (71) routing algorithm that (72) work done on theOSI IS-IS intradomain routing protocol. This routing, as compared to distance-vector routing,requires (73) processing power. The (74) algorithm is used to calculate mutes. OSPFrouting table updates only take place when necessary, (75) at regular intervals.

A．but rather
B．rather too
C．rather than
D．rather that