引起主动脉瓣关闭不全的病因是（）

A.风湿性心脏病

B.主动脉夹层动脉瘤

C.马方综合征

D.细菌性心内膜炎

E.以上都是

The least accurate statement about measures of dispersion for a distribution is that the:（）

A. range provides no information about the shape of the data distribution.

B. mean absolute deviation will always be smaller than the standard deviation.

C. arithmetic average of the deviations around the mean will always be equal to one.