Which codec standard requires a bit rate of 64 kbps to maintain a mean opinion score of 4.1？（）

A.TCP header compression on router R1
B.TCP header compression on router R2
C.RTP header compression on router R1
D.RTP header compression on router R2
E.payload header compression on router R1
F.payload header compression on router R2

A.in class class-default, replace fair-queue with bandwidth remaining percent 50 
B.in class autoqos-transactional-Fa0/1, replace bandwidth remaining percent 40 with bandwidth remaining percent 20 
C.in class autoqos-transactional-Fa0/1, replace bandwidth remaining percent 40 with bandwidth remaining percent 30 
D.in class autoqos-Bulkl-Fa0/1, replace bandwidth remaining percent 19 with bandwidth remaining percent 25 
E.in class autoqos-Scavenger-Fa0/1, replace bandwidth remaining percent 1 with bandwidth remaining percent 10 
F.in class autoqos-Signaling-Fa0/1, replace bandwidth remaining percent 4 with bandwidth remaining percent 1 

A.the routing protocols being utilized in the network
B.the applications utilizing the network
C.the traffic destinations
D.network addressing scheme
E.cost of implementation
F.the amount of the control needed of the resources