H.248协议中以下哪个是MG发给MGC的心跳消息？（ ）
A.!/1 [192.168.6.71]:2944 Transaction=5{Context = - {Auditcapability = A0 {Audit{Media,packages}}}}
B.!/1 [192.168.6.71]:2944 Transaction=20{Context = -{AuditValue=ROOT{Audit{}}}}
C.!/1 [191.2.6.213]:2944 Transaction=275{Context=-{Notify=ROOT{ObservedEvents=0{19700101T011 53516:it/ito}}}}
D.!/1 [192.168.1.119]:2944 Transaction = 2050{Context = -{AuditValue=ROOT{Audit{Packages}}}}
正确答案是C