Chapter 8.4, Problem 69E

To determine

The correct statements out of the following statements:

(A): The power grid frequency was at or below the mean until late $1999$.

(B): The power grid frequency, was more stable in mid-$1999$ than in $1995$.

(C): The power grid frequency, was more stable in mid-$2002$ than in $1999$.

(D): The greatest fluctuations in the power grid frequency occurred in $2000-2001$.

(E): The power grid frequency was more stable around January $1995$ than around January $1999$.

If the chart shows the approximate standard deviation of the power grid frequency, in $\frac{1}{1000}$ cycles per second, for over $6$-month periods and $0.9$ is the average standard deviation.