TheAPIchangesshouldprovidebothsourceandbinary()forprogramswrittentotheoriginalAPI.Thatis,existingprogrambinariesshouldcontinuetooperatewhenrunonasystemsupportingthenewAPI.Inaddition,existing()thatarere-compiledandrunonasystemsupportingthenewAPIshouldcontinuetooperate.Simplyput,theAP(I)formulticastreceiversthatspecifysourcefiltersshouldnotbreakexistingprograms.ThechangestotheAPIshouldbeassmallaspossibleinordertosimplicitythetaskofconvertingexisting(_______)receiverapplicationstousesourcefilters.Applicationsshouldbeabletodeletewhenthenew()filterAPIsareunavailable(e.g.,callsfailwiththeENOTSUPPerror)andreactgracefully(e.g.,reverttooldnon-source-filterAPIordisplayameaningfulerrormessagetotheuser). 横线处应选()。
A.multicast
B.unicast
C.broadcast
D.anycast
正确答案是A