单项选择题

A、缺货率=缺货的单品数×总销售单品数×100%
B、缺货率=缺货的单品数∕总销售单品数×100%
C、缺货率=缺货天数∕卖货天数×100%
D、缺货率=缺货天数×卖货天数×100%