Which of the following statements about interpreting standard deviation is true?

a. the empirical rule can't be applied unless the frequency distribution is mound-shaped and symmetric. chebyshev's rule can be applied to any data set, regardless of the shape of its frequency distribution.

b. chebyshev's rule can't be applied unless the frequency distribution is mound-shaped and symmetric. the empirical rule can be applied to any data set, regardless of the shape of its frequency distribution.

c. neither chebyshev's rule nor the emprical rule require any assumptions about the frequency distribution.

d. neither the empirical rule nor chebyshev's rule can be applied to data unless the frequency distribution is mound-shaped and symmetrical.