BSC话务掉话比计算公式为______。（ ）
A.MC380a/3600*60/(MC14c+MC621+MC736+MC739)
B.(MC380a+MC380b)/3600*60/(MC14c+MC621+MC736+MC739)
C.(MC380a+MC380b)/60/(C182＋MC663－C103)
D.MC380a/3600*60/(C182＋MC663－C103)
正确答案是C