[单选] Which one is correct about severity？关于严重度，下列说法正确的是？a．It is the rank associated with the most serious effect for a given failure mode填写失效模式最严重影响的评价等级b．It is the rank associated with the least serious effect for a given failure mode填写失效模式最小严重影响的评价等级c．It is the rank associated with the average serious effect for a given failure mode填写失效模式影响的平均评价等级d． All of the above are not correct以上说法都不正确