7.2 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. arithmetic average of the deviations around the mean will be equal to one.
C. mean absolute deviation will be either less than or equal to the standard deviation
B在不是normal distribution的情况下为什么会等于0？
C在怎么推导
