Which of the Following Is Not a Good Rule of Thumb

Which of the following is not a good rule of thumb for data values exhibiting a normal distribution?

A) Approximately 95% of the values lie within two standard deviations of the mean.
B) Approximately two-thirds of the values lie within one standard deviation of the mean.
C) Exactly half of the values lie at or above the mean.
D) Exactly half of the values lie within one standard deviation of the mean.