在Rt△ABC中，∠C=90°，BC=3，AC=4，点D在斜边AB上,且满足DC²=DA·DB；则DB＝     

An analysis determined that approximately 99 percent of the observations of daily sales for a company were within the interval from $ 250000 to $ 580000 and that daily sales for the company were normally distributed. The mean daily sales and standard deviation of daily sales, respectively, for the company were closest to: Mean daily sales Standard deviation of daily sales（）

A. $ 415000 $ 41667

B. $ 415000 $ 55000

C. $ 355115 $ 41667