Standard deviation is zero

The standard deviation of a data set is $$0$$, Which of the statements must be true?

A. The data set is empty.

B. The mean of the data set is $$0$$.

C. The data elements are all unique and there is a constant difference between all of the elements.

D. The sum of the differences between each element and the mean is zero.

E. All of the data elements are equal to $$0$$.

F. Half of the data elements are positive and half are negative.

G. All of the data elements have the same value.

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