When analyzing categorical data, stem and leaf display is an appropriate plot.

X is a discrete random variable that can have values from 0 to infinity, and occurrences of the events X counts are independent. The standard deviation of X is equal to the square root of the mean. The probability distribution of X is a(n) （）distribution.

A.binomial
B.uniform
C.normal
D.Possion

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The empirical rule tells us that approximately of the values cluster within a distance of 1 standard deviation from the mean for a bell-shaped distribution（）

A.68%
B.95%
C.99.7%
D.none of the above

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