單項選擇題

某地市購買IP話機,數(shù)量如下: 
VVX1500:10部 
CP7975:30部  
C.CP7911:50部  
D.CP7906:100部 
在購買話機的同時,需要購買的話機許可DLU數(shù)量為:()

A.510
B.550
C.560
D.660

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