A.WithIGMPvl，queriesaresenttoaspecificgroup
B.HostsissuingIGMPvlrequestswillbecorrectlyinterpretedbyIGMPv2hostsduetobackwardcompatibility
C.AnIGMPv2routerwillignoreIGMPv2leavemessageswhenIGMFVlhostsarepresent
D.WithIGMFV2，aleavemessageissupported
E.AnIGMPv2hostwillsendanIGMFVlreportonanIGMFVlrouter
F.AnIGMPv2routercanonlyallowIGMPv2hoststoexecuteajoinrequest
正确答案：参考C, D, E
